Get rid of buggy System.halt/2

Closes #1515, thanks to @AtKaaZ for debugging and pinpointing
this function as the root cause for output issues on Windows.
Update CONTRIBUTING.md

Feature requests should be discussed over the core mailing list.
Remove old mix artifacts without a need for force or changes
always remove unmatched beam files when compiling
Fixed problem with elixir.bat removing exclamation marks from command line
Merge pull request #1517 from ToJans/master

Fixed problem with elixir.bat removing exclamation marks from command line
Fixing doc typos in File
Add &local/arity and &Remote.fun/arity
Deprecate function/1 and function/3
Merge pull request #1519 from jwarwick/file_typos

Fixing doc typos in File
Allow &() as a general capture mechanism
Fix Macro.to_string with &
Allow &1.foo syntax inside capture
Fix Stream bugs and add more composing tests

Fix Stream.take_while looping infinitely when given lazy stream.
Fix Stream.take and Stream.take_while calling fun one extra time.
Add more tests where Stream functions are given streams.
Merge pull request #1521 from ericmj/stream-fixes

Fix Stream bugs and add more composing tests
Normalize and allow captures in Regex.scan/3, closes #1526
Fixed doc typos in Regex
Merge pull request #1528 from jwarwick/regex_typos

Fixed doc typos in Regex
Fix issue with nested binaries in Macro.to_string/1, closes #1522
Fixed doc typos in Macro