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
Improve error messages
Unicode split
Update binary_to_ macros to use binary_to_ functions in R16B.

Also add support for float_to_binary/2
Include more recent Erlang versions into Travis-CI configuration
Merge pull request #914 from yrashk/binary_to_updates

Update binary_to_ macros to use binary_to_ functions in R16B.
Improve documentation for the String module
Make record types in record public as well
Improve docs for function
Add documentation on @record_fields and @record_types to defrecord
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...