Added weather nodes

Added the weather input and query nodes. Comments are welcome.
I think the presentation of this can be tidied up. Something like:

---

The node sets the following properties of `msg.payload`:

 - <b>description</b> - a brief description of the weather
 - <b>weather</b> - a blah blah blah
 - <b>and</b> - ...
 - <b>so</b> - ...
 - <b>on</b> - ...