return the deferred that $.ajax returns when making ajax calls
Explicitly return null when web sockets are used, in addition to returning the deferred object that $.ajax returns. Document changes related to return.
Merge branch 'return-deferreds' of https://github.com/akinnee/jquery.jsonrpcclient.js into akinnee-return-deferreds

Conflicts:
	jquery.jsonrpcclient.js