Fixes #99. Removes ancient readline and custom tab completion code in favor of native + std rlcompleter.

[awwad]

Please see comments in Issue #99.

Synopsis:

• Prior to this change, in order to provide tab completion in a seash session on OS X (which ships a somewhat crippled non-GNU readline with Xcode python), we shipped an old readline.so.mac library with seash, and also a tab_completer.py custom module, with some minor integration code involving a hot file rename. ^_^
• Unfortunately, that readline.so.mac library has a bug (see here) that results in a nonsense escape character being spat out to stdout anytime readline is imported. This caused some problems for utf, which detected that as test failure anytime readline was imported.

This change removes all that and instead just uses whatever native readline is available on *nix or OS X, and imports rlcompleter to handle tab completion. Yay for less code!

[awwad]

All tests that should pass pass locally (3 failures: ut_seash_getrelease.py, ut_seash_getrelease_insecure.py, ut_seash_moduleconflicterror.py - just as with vanilla). I no longer get the blank false failures on my OS X laptop.

If PR #98 were merged, the tests via AppVeyor and Travis would occur and show up here.

[awwad]

This change also breaks tab completion of local files / folders, which I hadn't previously understood. /:

> loadkeys ~/<TAB>

should provide completion but does not there. Will have to try fixing the code to work with it and issue another PR. (Confusion stemmed from fact that filename tab completion is only available following a command, not on bare line - e.g. > sea<TAB> doesn't display seash.py.)