Merge pull request #1098 from alco/path-expand-doc

Fix behavior of Path.expand/2. Improve docstrings
Improve error messages when there is a space in between function name and parenthesis
Remove empty? from the Enum protocol, closes #1097
Deprecate Code.eval in favor of Code.eval_string, closes #953
Consider load time on ExUnit reports, closes #893
Support MIX_PATH as alternative load paths, closes #889
Update CHANGELOG
Do not raise if a dependency can't be found, closes #1052
Add initial support for .iex files
Use System.halt instead of :erlang.halt
Don't wrap Code.require_file
Include description of .iex in the doc for IEx