Squashed 'bogo/' changes from ddf39b9..c815ff7

c815ff7 Merge pull request #16 from BoGoEngine/separators
dc278e8 Support separator in process_sequence()
edb6486 Explain the etymology for BoGo

git-subtree-dir: bogo
git-subtree-split: c815ff75721f96a4ba3d90880a070c9089e37337
Merge commit '9253b99e2dd64f2690316811bf8f8cca218e56f8'
Support undoing previous words with backspace

Now that process_sequence() has acquired support for separators, we
don't need to reset() on unaccepted chars. We just keep them in the raw
sequence and the committed string. So they can get pretty long like
this:
sequence = 'con meof ddieen'
committed string = con mèo điên'

As such, it is now even possible to undo the grave tone in mèo.