Implement Mix.Version, closes #1115
implement mix package and related tasks re #1124
changes from PR discussion

1: ensure_loaded?

3: ebin

2: assume path/ebin to be packaged

6: accept project path & assume ebin

8: include priv in archive

5: local.uninstall handles packages too

7: local.install [] will install a package

7: mix new .gitignore *.ez files
local.uninstall warn on uninstall package task
Fix typo in doc
Merge pull request #1256 from mururu/fix-typo

Fix typo in doc
Handle --warnings-as-errors and other elixirc options in mix compile
Update CHANGELOG
Merge pull request #1130 from meh/mix-version

Implement Mix.Version
Fix Dict.drop documentation
Remove documentation of .split, .drop and .take on HashDict and ListDict

They are already documented on Dict
Avoid usage of defrecordp and move all parsing to Mix.Version.Parser
Merge pull request #1258 from elixir-lang/fix-typo

Review documentation of `.split`, `.drop` and `.take` on `Dict`
Merge pull request #1223 from jeremyjh/1124-mix-local-arch

add mix package and related tasks
Rename packages to archives
Update CHANGELOG
Uniform use of whitespace after commas on codebase

This make easier to read and also follow some standard in the code
Merge pull request #1259 from elixir-lang/whitespaces

Uniform use of whitespace after commas on codebase
Update docs for Macro.expand
Update CONTRIBUTING.md language