Add option to pass headers to $.ajax method
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.
document options for instantiating a new $.JsonRpcClient
Merge branch 'headers-option' of https://github.com/akinnee/jquery.jsonrpcclient.js into akinnee-headers-option

Conflicts:
	jquery.jsonrpcclient.js
Merge branch 'return-deferreds' of https://github.com/akinnee/jquery.jsonrpcclient.js into akinnee-return-deferreds

Conflicts:
	jquery.jsonrpcclient.js
Merge branch 'master' of github.com:Textalk/jquery.jsonrpcclient.js into dev-coveralls
Adding travis and coverall badges.