Add a hook for the keyring module
Add comments to keyring hook
Add hook for keyring package.

Python keyring package:
https://pypi.python.org/pypi/keyring
Add test for keyring package.
Add license to hook file.
Add license to test, as well.
Merge branch 'rhymeswithcycle-keyring-hook' into issue-1101
Merge branch 'hook-keyring' of https://github.com/rbranche/pyinstaller into issue-1101

Conflicts:
	PyInstaller/hooks/hook-keyring.py
Move test into interactive/, as it it an interactive one.
Add a new test for keyring, checking by using a .toc.
Rename hook-keyring.py to hook-keyring.backends.py.
Close issue #1101: Add a hook for the keyring library.