Add cover support to mix test
Do not run cover tests before R16
Improve error message on unclosed interpolation/string, closes #794
Support --help and -h in elixir and iex, closes #854
Fail if an application can't be started, closes #869
Add Path.t (for input types) and Path.r (for output), closes #873
Revert "IEx autocompletion should show all exported functions, not only documented ones"

This reverts commit 3ffc5e9e8497cac9312dc02dbb8f763b9ee9edf7.

Closes #879.