drop ok tag from cast() responses, update docs (cherry picked from commit 23bc964bdd8b89be9af53cdd4da53603fe2edb3f)

diff --git a/src/rexi.erl b/src/rexi.erl
index fd195a2..0eaa324 100644
--- a/src/rexi.erl
+++ b/src/rexi.erl
@@ -14,7 +14,8 @@
 restart() ->
     stop(), start().
 
--spec cast(node(), mfa()) -> {ok, reference()}.
+%% @equiv cast(Node, self(), MFA)
+-spec cast(node(), mfa()) -> reference().
 cast(Node, MFA) ->
     cast(Node, self(), MFA).
 
@@ -22,14 +23,14 @@
 %% You might want to use this instead of rpc:cast/4 for two reasons.  First,
 %% the Caller pid and the returned reference are inserted into the remote
 %% process' dictionary as `rexi_from', so it has a way to communicate with you.
-%% Second, the remote process is monitored. If it dies, Caller will receive a
-%% message of the form `{rexi_EXIT, Ref, Reason}' where Ref is the returned 
-%% reference and Reason is the exit reason.
--spec cast(node(), pid(), mfa()) -> {ok, reference()}.
+%% Second, the remote process is monitored. If it exits with a Reason other
+%% than normal, Caller will receive a message of the form
+%% `{rexi_EXIT, Ref, Reason}' where Ref is the returned reference.
+-spec cast(node(), pid(), mfa()) -> reference().
 cast(Node, Caller, MFA) ->
     Ref = make_ref(),
     ok = gen_server:cast({?SERVER, Node}, {doit, {Caller,Ref}, MFA}),
-    {ok, Ref}.
+    Ref.
 
 %% @doc Sends an async kill signal to the remote process associated with Ref.
 %% No rexi_EXIT message will be sent.