Adds symlink to File

implementation of feature request #2114
Create remote funs even in &mod.fun/arity, closes #2133
Merge pull request #2123 from duksis/symlink_on_file

Adds symlink to File
Rename symlink to ln_s according to File's convention
Use rebar hosted on S3
Ensure aliases are respected on root, closes #2227
Improve docs for generated apps
Use Exception.message/1 instead of exception.message
Update CHANGELOG
Soft deprecate is_exception/1 in favor of Exception.exception?/1
Convert ExUnit.Test and ExUnit.TestCase to structs