[aprssig] APRS Symbols update

[Robert Bruninga]

New APRS symbols defined:

Boyd, K5YKG carefully compared all symbol set documents and
identified some minor corrections to the main APRS 1.1 symbol
set document but also suggested some new ones.  I have also
added some definitions to some of the overlay characters such as
the following:

Added three new overlay series:

\% - Powerplants (with Overlays. N= Nuclear for example)
\8 - Nodes with overlays.  Example, "G8" would be 802.11G
\H - \H is HAZE but other overlays are now HAZARDs. WH is
"H.Waste"

Added some new definitions to overlays on these existing overlay
symbols:

\u - Overlay Trucks.  "Tu" is a tanker. "Gu" is a gas truck, etc
\< - Advisories may now have overlays
\[ - \[ is wall cloud, but overlays are humans. "S[" is a skier,
etc.
\h - is a building. "\h" is a Ham store, "Hh" is Home Depot,
etc.

These overlay definitions are found in:
http://www.ew.usna.edu/~bruninga/aprs/symbols-new.txt

The original Primary and Alternate symbols are defined in:
http://www.ew.usna.edu/~bruninga/aprs/symbolsX.txt

I hope that covers most of the requests that have accumulated
recently.

Enjoy.
Bob, WB4APR