ARROW-4482: [Website] Add blog archive page

The /blog/ page now looks like this:

![image](https://user-images.githubusercontent.com/2975928/78726737-96bd7a80-78e7-11ea-976c-9bd2efa39e60.png)

Closes #52 from nealrichardson/blog-list and squashes the following commits:

4bb5dea4 <Neal Richardson> Add translations as a post attribute so we can show it on the blog list
937da077 <Neal Richardson> Delete unused template
977371f0 <Neal Richardson> Clean up blog list presentation
1d392122 <Neal Richardson> Experimenting with a blog list page

Authored-by: Neal Richardson <neal.p.richardson@gmail.com>
Signed-off-by: Wes McKinney <wesm+git@apache.org>
diff --git a/_config.yml b/_config.yml
index 15cdd4d..5f647b7 100644
--- a/_config.yml
+++ b/_config.yml
@@ -17,7 +17,7 @@
 permalink: /blog/:year/:month/:day/:title/
 repository: https://github.com/apache/arrow
 destination: build
-excerpt_separator: ""
+excerpt_separator: </p>
 timezone: America/New_York
 
 kramdown:
diff --git a/_includes/blog_entry.html b/_includes/blog_entry.html
deleted file mode 100644
index 65ec138..0000000
--- a/_includes/blog_entry.html
+++ /dev/null
@@ -1,20 +0,0 @@
-{% comment %}
-Licensed to the Apache Software Foundation (ASF) under one or more
-contributor license agreements.  See the NOTICE file distributed with
-this work for additional information regarding copyright ownership.
-The ASF licenses this file to you under the Apache License, Version 2.0
-(the "License"); you may not use this file except in compliance with
-the License.  You may obtain a copy of the License at
-
-http://www.apache.org/licenses/LICENSE-2.0
-
-Unless required by applicable law or agreed to in writing, software
-distributed under the License is distributed on an "AS IS" BASIS,
-WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-See the License for the specific language governing permissions and
-limitations under the License.
-{% endcomment %}
-  <div class="blog-post" style="margin-bottom: 4rem">
-    {% include blog_header.html %}
-    {{ post.content }}
-  </div>
diff --git a/_includes/blog_header.html b/_includes/blog_header.html
index d12fd5f..233862d 100644
--- a/_includes/blog_header.html
+++ b/_includes/blog_header.html
@@ -16,7 +16,6 @@
 {% endcomment %}
 <h1>
   {{ post.title }}
-  <a href="{{ site.baseurl }}{{ post.url }}" class="permalink" title="Permalink">∞</a>
 </h1>
 
 {% capture discard %}
@@ -56,4 +55,12 @@
   {% else %}
     {{ post.author }}
   {% endif %}
+
+  {% if post.translations %}
+    <br />
+    <span class="badge badge-secondary">Translations</span>
+    {% for trans in post.translations %}
+      <a href="{{ site.baseurl }}/blog/{{ trans.url }}">{{ trans.language }}</a>
+    {% endfor %}
+  {% endif %}
 </p>
diff --git a/_posts/2017-05-08-0.3-release-japanese.md b/_posts/2017-05-08-0.3-release-japanese.md
index 6bad5ad..1d929fb 100644
--- a/_posts/2017-05-08-0.3-release-japanese.md
+++ b/_posts/2017-05-08-0.3-release-japanese.md
@@ -4,6 +4,9 @@
 date: "2017-05-08 00:00:00 -0400"
 author: wesm
 categories: [release,translation]
+translations:
+  - language: 原文(English)
+    url: 2017/05/08/0.3-release/
 ---
 <!--
 {% comment %}
@@ -24,8 +27,6 @@
 {% endcomment %}
 -->
 
-[原文(English)]({% post_url 2017-05-08-0.3-release %})
-
 Apache Arrowチームは0.3.0のリリースをアナウンスできてうれしいです。2月にリリースした0.2.0から10週間の活発な開発の結果が今回のリリースです。[**23人のコントリビューター**][14]が[**306個のJIRAのissueを解決**][1]しました。
 
 複数のArrowの実装にたくさんの新しい機能を追加しています。2017年、特に注力して開発するのは、インメモリー用のフォーマット、型のメタデータ、メッセージング用のプロトコルです。これは、ビッグデータアプリケーションに**安定していてプロダクションで使える基盤**を提供するためです。高性能IOとインメモリーデータ処理にArrowを活用するために、[Apache Spark][3]・[GeoMesa][2]コミュニティーと協力していてとてもエキサイティングです。
diff --git a/_posts/2017-05-08-0.3-release.md b/_posts/2017-05-08-0.3-release.md
index cf38a8b..8ea3f4a 100644
--- a/_posts/2017-05-08-0.3-release.md
+++ b/_posts/2017-05-08-0.3-release.md
@@ -4,6 +4,9 @@
 date: "2017-05-08 00:00:00 -0400"
 author: wesm
 categories: [release]
+translations:
+  - language: 日本語
+    url: 2017/05/08/0.3-release-japanese/
 ---
 <!--
 {% comment %}
@@ -24,8 +27,6 @@
 {% endcomment %}
 -->
 
-Translations: [日本語]({% post_url 2017-05-08-0.3-release-japanese %})
-
 The Apache Arrow team is pleased to announce the 0.3.0 release of the
 project. It is the product of an intense 10 weeks of development since the
 0.2.0 release from this past February. It includes [**306 resolved JIRAs**][1]
diff --git a/_posts/2019-09-30-introducing-arrow-flight-japanese.md b/_posts/2019-09-30-introducing-arrow-flight-japanese.md
index a4c8c70..1ffba35 100644
--- a/_posts/2019-09-30-introducing-arrow-flight-japanese.md
+++ b/_posts/2019-09-30-introducing-arrow-flight-japanese.md
@@ -5,6 +5,9 @@
 date: "2019-10-13 00:00:00 -0600"
 author: wesm
 categories: [application,translation]
+translations:
+  - language: 原文(English)
+    url: 2019/10/13/introducing-arrow-flight/
 ---
 <!--
 {% comment %}
@@ -25,8 +28,6 @@
 {% endcomment %}
 -->
 
-[原文(English)]({% post_url 2019-09-30-introducing-arrow-flight %})
-
 この1.5年、Apache Arrowコミュニティーは**Flight**の設計と実装を進めてきました。Flightは高速なデータトランスポートを実現するための新しいクライアント・サーバー型のフレームワークです。Flightを使うとネットワーク越しに大きなデータセットを送る処理を簡単に実現できます。Flightは特定用途向けに設計されたものではないため、幅広い用途で利用できます。
 
 Flightの実装は、まず、[gRPC][1]を使ったArrow列指向フォーマット(つまり「Arrowレコードバッチ」)のトランスポートの最適化に注力しました。gRPCはGoogleが開発しているHTTP/2ベースのRPCライブラリー・フレームワークで、広く利用されています。gRPCも特定用途向けではなく幅広い用途で使えるように設計されています。これまでFlightをgRPCベースで実装することに注力してきましたが、gRPCでだけ使えるようにしたいわけではありません。
diff --git a/_posts/2019-09-30-introducing-arrow-flight.md b/_posts/2019-09-30-introducing-arrow-flight.md
index 8fdc4c0..d59bf5f 100644
--- a/_posts/2019-09-30-introducing-arrow-flight.md
+++ b/_posts/2019-09-30-introducing-arrow-flight.md
@@ -7,6 +7,9 @@
 date: "2019-10-13 00:00:00 -0600"
 author: wesm
 categories: [application]
+translations:
+  - language: 日本語
+    url: 2019/10/13/introducing-arrow-flight-japanese/
 ---
 <!--
 {% comment %}
@@ -27,8 +30,6 @@
 {% endcomment %}
 -->
 
-Translations: [日本語]({% post_url 2019-09-30-introducing-arrow-flight-japanese %})
-
 Over the last 18 months, the Apache Arrow community has been busy designing and
 implementing **Flight**, a new general-purpose client-server framework to
 simplify high performance transport of large datasets over network interfaces.
diff --git a/blog.html b/blog.html
index ddabcea..8cb4500 100644
--- a/blog.html
+++ b/blog.html
@@ -26,6 +26,22 @@
 
 {% for post in site.posts %}
   {% unless post.categories contains 'translation' %}
-    {% include blog_entry.html %}
+  <p>
+    <h3>
+      <a href="{{ site.baseurl }}{{ post.url }}">{{ post.title }}</a>
+    </h3>
+    {% if post.translations %}
+      <em>Translations:</em>
+      {% for trans in post.translations %}
+        <a href="{{ site.baseurl }}/blog/{{ trans.url }}">{{ trans.language }}</a>
+      {% endfor %}
+    {% endif %}
+    <p>
+    <span class="blog-list-date">
+      {{ post.date | date: "%-d %B %Y" }}
+    </span>
+    </p>
+    {{ post.content | strip_html | truncatewords: 50 }}
+  </p>
   {% endunless %}
 {% endfor %}
diff --git a/css/main.scss b/css/main.scss
index c9e24a3..14f202f 100644
--- a/css/main.scss
+++ b/css/main.scss
@@ -3,3 +3,8 @@
 
 @import "bootstrap";
 @import "font-awesome";
+
+.blog-list-date {
+  color: #888888;
+  font-style: italic;
+}