Fix rebar config scripts evaluation

Scripts are evaluated using the dependency directory as current directory

Closes #1262
Merge pull request #1264 from edgurgel/mix-rebar-scripts

Fix rebar config scripts evaluation
Do not check in utf8 directories into source control
Make sure all Erlang parameters are extracted and parsed in elixir.bat
Refactoring of some mix tasks
Added parameter validation in the elixir.bat file

The batch file now allows both erlang and elixir commands before the ".ex" file; if any unknown parameter is passed before the ".ex file", an error is thrown.
Removeved the echo prefix from the elixir.bat file

Inline editing in github is dangerous!
Clean up error messages, move defaults warning to an error
Avoid clash in between modules
Update CHANGELOG
Merge pull request #1269 from ToJans/master

On Windows Erlang parameters were not getting passed to elixir.bat in a proper way
elixir.bat only worked from the bin folder

Apparently, when shifting parameters, the %~dp0 is not preserved, 
so it needs to keep this value. This will fix things like iex on Windows, which just crashed with the previous version.
Update executable docs
Merge pull request #1270 from ToJans/master

With the new elixir.bat version the batch script only worked from the ./bin folder on windows
Update CHANGELOG
Make sure we don't receive an EXIT message from the dependency tracker

It pollutes IEx and scripts execution

Signed-off-by: José Valim <jose.valim@plataformatec.com.br>
Fixed grammar and wrong word (exit, not exist) in Process.exit/2 documentation.
Merge pull request #1273 from rnowling/master

Fixed grammar and wrong word (exit, not exist) in Process.exit/2 documentation.
Use proper path separator in msys

For now, we are only checking the path on msys but
we may need to check it for cygwin too.

Thanks to @ToJans for providing guidance and debug
information to sort this issue out.
Use = instead of == on shell comparison