Add vcpkg support with proper CMake installation and package config

- Add proper install(TARGETS) command for the casbin library
- Add install(EXPORT) to generate and install CMake config files
- Create casbinConfig.cmake.in for proper package discovery
- Use GNUInstallDirs for standard installation paths
- Change include directories and link libraries from PRIVATE to PUBLIC
- Add generator expressions for BUILD_INTERFACE and INSTALL_INTERFACE
- Create casbinConfigVersion.cmake with version compatibility checking
- All tests pass successfully

Co-authored-by: nomeguy <85475922+nomeguy@users.noreply.github.com>

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index cf6415b..698a0c7 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -170,21 +170,61 @@
 # Install casbin
 
 if(CASBIN_INSTALL)
+    include(GNUInstallDirs)
+    include(CMakePackageConfigHelpers)
+    
     message(CHECK_START "[casbin]: Installing casbin ...")
-    export(
+    
+    # Install the library
+    install(
         TARGETS casbin
-        NAMESPACE casbin::
-        FILE casbinConfig.cmake
+        EXPORT casbinTargets
+        ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
+        LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
+        RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
     )
-
+    
     # Installing headers
     install(
         DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/include/casbin
-        DESTINATION include
+        DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
     )
-
-    set(CMAKE_EXPORT_PACKAGE_REGISTRY ON)
-    export(PACKAGE casbin)
+    
+    # Install the export set
+    install(
+        EXPORT casbinTargets
+        FILE casbinTargets.cmake
+        NAMESPACE casbin::
+        DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/casbin
+    )
+    
+    # Create and install the config file
+    configure_package_config_file(
+        ${CMAKE_CURRENT_SOURCE_DIR}/cmake/casbinConfig.cmake.in
+        ${CMAKE_CURRENT_BINARY_DIR}/casbinConfig.cmake
+        INSTALL_DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/casbin
+    )
+    
+    # Create and install the version file
+    write_basic_package_version_file(
+        ${CMAKE_CURRENT_BINARY_DIR}/casbinConfigVersion.cmake
+        VERSION ${PROJECT_VERSION}
+        COMPATIBILITY SameMajorVersion
+    )
+    
+    install(
+        FILES
+            ${CMAKE_CURRENT_BINARY_DIR}/casbinConfig.cmake
+            ${CMAKE_CURRENT_BINARY_DIR}/casbinConfigVersion.cmake
+        DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/casbin
+    )
+    
+    # Export for build tree (optional, for developers)
+    export(
+        EXPORT casbinTargets
+        FILE ${CMAKE_CURRENT_BINARY_DIR}/casbinTargets.cmake
+        NAMESPACE casbin::
+    )
 
     message(CHECK_PASS " The targets can now be imported with find_package(casbin)")
     message(STATUS "[casbin]: Build the \"install\" target and add \"${CMAKE_INSTALL_PREFIX}/include\" to you PATH for casbin to work")

casbin/CMakeLists.txt

diff --git a/casbin/CMakeLists.txt b/casbin/CMakeLists.txt
index cc51e16..c242791 100644
--- a/casbin/CMakeLists.txt
+++ b/casbin/CMakeLists.txt
@@ -76,8 +76,12 @@
 add_library(casbin STATIC ${CASBIN_SOURCE_FILES})
 
 target_precompile_headers(casbin PRIVATE ${CASBIN_INCLUDE_DIR}/casbin/pch.h)
-target_include_directories(casbin PRIVATE ${CASBIN_INCLUDE_DIR})
-target_link_libraries(casbin PRIVATE nlohmann_json::nlohmann_json)
+target_include_directories(casbin 
+    PUBLIC 
+        $<BUILD_INTERFACE:${CASBIN_INCLUDE_DIR}>
+        $<INSTALL_INTERFACE:include>
+)
+target_link_libraries(casbin PUBLIC nlohmann_json::nlohmann_json)
 
 set_target_properties(casbin PROPERTIES 
     PREFIX ""

cmake/casbinConfig.cmake.in

diff --git a/cmake/casbinConfig.cmake.in b/cmake/casbinConfig.cmake.in
new file mode 100644
index 0000000..d9f3e29
--- /dev/null
+++ b/cmake/casbinConfig.cmake.in
@@ -0,0 +1,25 @@
+#  Copyright 2020 The casbin Authors. All Rights Reserved.
+#
+#  Licensed 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.
+
+@PACKAGE_INIT@
+
+include(CMakeFindDependencyMacro)
+
+# Find required dependencies
+find_dependency(nlohmann_json 3.10.1 REQUIRED)
+
+# Include the targets file
+include("${CMAKE_CURRENT_LIST_DIR}/casbinTargets.cmake")
+
+check_required_components(casbin)