Support reading mustache 'lists' from files

This commit add support for reading mustache 'lists' from files, so you
can use the list section functionality when templating things.

An example of the list syntax is as follows:

{package_commands, {list, [[{name, "riak"}], [{name, "riak-admin"}], [{name, "search-cmd"}]]}}.

Then you can, for each of the list elements, render some text:

{{#package_commands}}
chmod +x bin/{{name}}
{{/package_commands}}

src/rebar_templater.erl

@@ -81,6 +81,9 @@ resolve_variables([], Dict) ->
 resolve_variables([{Key, Value0} | Rest], Dict) when is_list(Value0) ->
     Value = render(list_to_binary(Value0), Dict),
     resolve_variables(Rest, dict:store(Key, Value, Dict));
+resolve_variables([{Key, {list, Dicts}} | Rest], Dict) when is_list(Dicts) ->
+    %% just un-tag it so mustache can use it
+    resolve_variables(Rest, dict:store(Key, Dicts, Dict));
 resolve_variables([_Pair | Rest], Dict) ->
     resolve_variables(Rest, Dict).
 
@@ -134,14 +137,14 @@ create1(Config, TemplateId) ->
                    undefined ->
                        Context0;
                    File ->
-                       case file:consult(File) of
-                           {ok, Terms} ->
-                               %% TODO: Cleanup/merge with similar code in rebar_reltool
-                               M = fun(_Key, _Base, Override) -> Override end,
-                               dict:merge(M, Context0, dict:from_list(Terms));
+                       case consult(load_file([], file, File)) of
                            {error, Reason} ->
                                ?ABORT("Unable to load template_vars from ~s: ~p\n",
-                                      [File, Reason])
+                                      [File, Reason]);
+                           Terms ->
+                               %% TODO: Cleanup/merge with similar code in rebar_reltool
+                               M = fun(_Key, _Base, Override) -> Override end,
+                               dict:merge(M, Context0, dict:from_list(Terms))
                        end
                end,
 
@@ -275,7 +278,7 @@ consult(Cont, Str, Acc) ->
             case Result of
                 {ok, Tokens, _} ->
                     {ok, Term} = erl_parse:parse_term(Tokens),
-                    consult([], Remaining, [Term | Acc]);
+                    consult([], Remaining, [maybe_dict(Term) | Acc]);
                 {eof, _Other} ->
                     lists:reverse(Acc);
                 {error, Info, _} ->
@@ -286,6 +289,13 @@ consult(Cont, Str, Acc) ->
     end.
 
 
+maybe_dict({Key, {list, Dicts}}) ->
+    %% this is a 'list' element; a list of lists representing dicts
+    {Key, {list, [dict:from_list(D) || D <- Dicts]}};
+maybe_dict(Term) ->
+    Term.
+
+
 write_file(Output, Data, Force) ->
     %% determine if the target file already exists
     FileExists = filelib:is_regular(Output),