Swap directions by hitting the shortcut a second time

I love this plugin, but I find it searching backwards to be more difficult than I'd like - I have to add a minus, and square brackets, etc. These changes (which include the commit in https://github.com/xavi-/sublime-selectuntil/pull/7) let you switch the search direction back and forth just by hitting the shortcut again.
Also included are some display fixes that work around bugs in Sublime's input panel (commit 7d04bda).