Added File.listdir API
Added File.listdir! variation
Fixed File.listdir! to return the list, without wrapping it in {:ok, _}
renamed to ls, added unit tests
File.ls & ls! tests now cover non-existent directory situation
Fix is_record tests to check tuple_size before accessing the first element
Unicode split
Check also Kernel.SpecialForms in h(). Fixes #906
Remove trailing whitespace in iex/helpers.ex
Replace length check with a check against []

length() is not constant time
Merge pull request #918 from alco/iex-h-fix

Make h() in IEx look at Kernel.SpecialForms too
Merge pull request #907 from devinus/fix-record-guard-for-tuples

Fix is_record tests to check tuple_size before accessing the first eleme...
Merge pull request #899 from n1rvana/master

Added File.ls & File.ls!
Merge pull request #909 from devinus/unicode-split

Unicode split
Improvements to File.ls implementation
Make h/2 and h/3 private in IEx.Helpers
Make s and t helpers private too
Fix an example in `lc` documentation
Fix a bug on Module.to_binary(Elixir), closes #920
Split IEx introspection functions into its own module