[aprssig] Garmin loans

[scott at opentrac.org]

Thanks to everyone who responded to my request - I'll be getting back to you
all individually soon.  I can't believe how much of a response I got!  I'll
be sorting through the offers and figuring out which models I need and when.

In related news, I figured out the (really poorly documented) custom symbol
upload function.  It won't work on all receivers, but for newer units like
the MAP 60C you can get an extra 24 symbols that exactly match the standard
16x16 APRS symbols.  I thought about having the tracker upload them itself,
but I think it's going to be simpler to just provide the bitmap files and
instructions on preparing the receiver.  It only takes a minute to update
the symbol set.

Scott
N1VG