#170 - fix repeat

Vintageous manages the 'repeat' command on its own to escape the 'undo' stack
tyranny. In Sublime Text, the 'repeat' command gets updates as you undo past
the current 'repeat' command.
#170 - fix redo

Vintageous has had trouble redoing for a while. All signs point at
'maybe_mark_undo_groups_for_gluing' as the culprit here. It seems that it
creates an entry of its own in the undo stack.

'maybe_mark_...' is being called every time just before an action is run.
Therefore, when you called 'yy', an undesired entry was created too, breaking
Ctrl+r.

To work around this problem, we now conditionally call 'maybe_mark_...' instead,
so, for instance, 'yy' never calls it any more.
edit changelog
Added tag 0.5.5 for changeset 8fbcd549b003