Fixes#307. Error is thrown when g:ycm_min_num_of_chars_for_completion
option is set to 0 user tries to delete an identifier which starts at
the beginning of the line.
This is for filename completion in the case of C-family include completion. The
path was being assembled incorrectly so os.isdir() was getting the wrong path
and then could not see was it a directory.
This was done by introducing a new ThreadedCompleter class that descends from
Completer. Both JediCompleter and FilenameCompleter descend from
ThreadedCompleter.
This implements the filename completer and introduces integration with
UltiSnips. The user will now see snippets in the completion menu. After
selecting a snippet, the user should invoke the UltiSnips trigger key
(which should be changed from the default of TAB) to trigger the snippet
expansion.
Fixes#77, Fixes#36
