Change createClient signature

- The new signature is:

  createClient(options, initCB), where
     - options is an optional object that defines different parameters such as
               display, etc.
     - initCB is an optional callback with the signature: function(err, display)
- The initCB is going to be called with an error ONLY if the connection to the X
  server fails. Further errors in the server connection will be 'emitted'.
- Update tests and test-runner.js accordingly.
- Update README.
Merge pull request #20 from santigimeno/new_create_client

Change createClient signature
version bump
QueryPointer result unpacking
Automatically send Render buffer if too large or before any GLX call
cleanup
remove debug output
use new createClient signature
version bump
err as first parameter in createClient cb
Update README.md