rtbl: Ease testing

Make testing easier with rtbl.BL.init mapping to add testing item to the
block list (locally).

Generate a hash:
>>> import hashlib
>>> test_hash = hashlib.sha256('user@example.org'.encode('utf-8')).hexdigest()

Then use it to pre-populate the block list:

>>> from sid.rtbl import RTBL, BL
>>> BL.init = {test_hash: 'For testing purposes'}