Remove special-case keybindings, bump version to 2.9.0

@dillonkearns @magnars @ruediger @ekyo @proofit404

Bumping everyone who's contributed (you are presumably the only users
at present). I'm removing the custom keybindings 'z' and 'i' in favour
of recommending they be customized if desired. As a friend pointed
out, these two special-cases take away from the "pure translation and
no more" aspect of god-mode. Case in point: I have a custom keybinding
for C-z to ido-switch-buffer and I'm interested in using a custom C-i
binding, I've always rebound these back in god-mode where otherwise I
wouldn't need to. Hope this change doesn't annoy you guys.

I've added in the README popular keybindings. I've tested these out
with emacs -Q and they work fine. If you're still using god-mode you
should check out this recent version as @dillonkearns's repeat support
made it behave perfectly now.

@dillonkearns I updated the test cases, but despite the keybinding
`2dx z' working fine on a test I did with "aabbcc" → "cc" (I just
tested it in this commit buffer, works fine), the cask test case runs
differently somehow and fails. Do you know why?