New chainable interface

[joelgriffith]

This makes it so a workflow like this:

chrome.goto('http://www...')
.then(() => chrome.type('input', 'foo'))
.then(() => chrome.type('input', 'bar'))
.then(() => chrome.click('.buy-now'))

Becomes

chrome
  .goto('http://www...')
  .type('input', 'foo')
  .type('input', 'bar')
  .click('.buy-now')

This new interface is still bw compatible with the old, however I had to hand-roll my own then which executes the actions. Internally this just queues actions until the then member is called. The ONLY gotcha is that anything that does new Chrome can't return it inside a promise-chain, otherwise the then method will be called and return undefined.

Thanks @mute for the tests, they helped tremendously here

[joelgriffith]

Forgot to add that this new interface also "retries" since a queue is being used. This allows us to do some cool things like not need pageload rarely (since a pageload will trigger an action failure, and it'll re-run)