Fix #202 implemented send_keys [ci skip]

I have a few troubles here.
1) When I try to call `trigger('focus')` event is actually triggered but input doesn't get real focus and keypressed buttons go somewhere else. But if I run that line https://github.com/jonleighton/poltergeist/commit/deda41fd7235ba8b82346d30daf1afb750318f66#L1R254 everything starts working. Ideas?
2) I see some code https://github.com/jonleighton/poltergeist/blob/202_send_keys/lib/capybara/poltergeist/client/agent.coffee#L117
https://github.com/jonleighton/poltergeist/blob/202_send_keys/lib/capybara/poltergeist/client/agent.coffee#L242
related to key/mouse events is that because at that moment there wasn't `sendEvent` function?