[aprssig] Adding Water Gage and VOLTS info to APRS

[Robert Bruninga]

To accomodate the addition of remote water gages to APRS,
two symbols have been designated for such use:

/w  is the water symbol
\w  is the flood symbol

Typically a water gage above flood stage would switch to the
flood symbol.  The water level is added as a fixed length
field of Fxxxx where xxxx is from -999 to +999 centimeters.

In addition, we are adding Vvvv for indicating volts in tenths.
Thus V128 would be 12.8 volts for this instrument.

Notice that this format is similar to that used for all WX
parameters, and since the APRS WX format is extensible,
these Fxxxx and Vvvv can be added to any existing
weather report without breaking anything.  Similarly,
when the specific water symbols are used, then only
the Fxxxx or optional Vvvv are needed, but an entire
weather report can also be added if additional isntruments
are available.

The proposed spec is shown on the APRS1.2 proposed
addendum page:

http://www.ew.usna.edu/~bruninga/aprs/watergage.txt

de Wb4APR, Bob