Packet Size being escaped

[lpercifield]

In testing with this library, there was a case where an Xbee packet was sent where the packet size byte was escaped. Looks like the simple hack is to add the isEscaped logic to the packet size switch.

[lpercifield]

lpercifield@0151e37

[kmark]

Thanks for this. I remember figuring out exactly how escaping worked (and when it wasn't necessary) took a lot of time and trial/error. Looks like I missed some things. If you send a PR I'll accept as-is since I'm not too worried about the code quality of this implementation at this point.