Refactor translation and comprehension building in two stages
Support nilly values and exceptions leaking in for filters
Improve comprehensions test suite
Make Mix.Utils.Underscore accept .'s and empty args
Made Mix.Utils.camelize handle empty string
Fix handling of raw rebar deps
Add map access
Only access public __struct__ function
Ensure structs can be access from context modules
Support binary generators
Forbid bit generators without size in comprehensions
Support :into in for comprehensions
Start migrating lc to for comprehensions
Migrate from bc to for comprehensions
Do not recognize undefined aliases as switches
Soft deprecate bc and lc
Add support for Enum.group_by/2.

Takes a collection and a function. The function takes a value and
returns a group for that value. The result is a map where the keys
are group values and the values are a list of elements from the
collection for which the function returned that particular
group value.
Minor style changes
Ensure variables can be defined in comprehensions
Correctly report test setup errors and dont run tests