File lstat implementation.

This is a straightforward cut and paste implementation of File.lstat and File.lstat! based on the File.stat implementation. It more or less implements the same functionality, but just uses the underlying erlang call
:file.read_link_info, rather than :file.read_file_info. 

- Booker C. Bense
We should create files in the tmp directory to avoid polluting the elixir checkout. Can you please amend the pull request?