added leafly and goatkcd plugins

added two additional plugins for siri:

* leafly -- invoked with .leafly or .weed, gets a given strain of marijuana from Leafly.com and outputs details on it.
* goatkcd -- invoked with .goatkcd or .xkcd, gets a random goatkcd.com comic. if given a comic number, will output that comic if it can be found. also has sfw option for goatkcd's sfw comic.