[aprssig] New MSG-OBJ format (rev b)

[Bob Bruninga]

> If you want,  you could also support a 3 character word, 
> but still to be a symbol, the first and last characters 
> must be [ and ].  A 3 character word/symbol is in the primary table, IMHO.

Help me here.  All symbols can be indicated with two bytes.  Did I miss
something?

Thanks
Bob, WB4APR