Move Elixir version mismatch to a warning, closes #1951
Rename Mix.Deps.Retriever to Mix.Deps.Loader
Unify deps.get and deps.update workflows
Do not erase elixir_compiler_pid
Update CHANGELOG
Consistently inline functions in the Kernel module by the compiler
Add Version.compare/2
Inline some process and node calls, closes #1808
Store Mix.Dep records in Mix.Dep.deps
Add Process.send/2 and Process.send_after/3
No longer compile unicode in parallel

Compiling in parallel only bought us 2s (out of 24s) since
compiling graphemes is what takes most of the time but it
considerably increases memory usage, by about 30%, since both
compilation targets are loaded into memory at once.
Clean up app.start tests
Raise on unknown dependencies for deps.get and deps.update
Ensure File.cp_r/3 respects trailing / in sources
Ensure doc_line resets algebra formatting line buffer, closes #2014
Remove pre-copying of dev dependencies

The current code was copying manifests but they got
recent access times which caused bugs. Also, a dependency
can have different results depending on each dependencies
are available and which are not, so simply copying the
compiled dep can lead to weird errors.
Add exception formatting and colorization to iex
Don't use Regex module inside Exception, as it may not be available
Respond to review comments
Document inlined functions are BIFs