Rename delay() to throttle, add new delay()

See also https://groups.google.com/d/msg/q-continuum/nOYkOcGeGL8/AQGjMrEyjKIJ

throttle() delays promises at most until the given time has passed since creating the promise. This is what delay() used to do.

delay() inserts a delay anywhere between resolutions (succeeded or rejected) in the promise chain. This is what jQuery users are used to, and it follows the [principle of least astonishment](http://en.wikipedia.org/wiki/Principle_of_least_astonishment) IMHO.