[Gpsbabel-code] Updated Garmin protocol spec

[Robert L. <rob...@us...>]

For those few that are brave enough to venture in here, Garmin has updated
their protocol spec.

	http://www.garmin.com/support/pdf/IOSDK.zip

I haven't fully diffed the specs, but at blush, it looks incremental.
There's very little earth shattering stuff in here, but wordings are
improved in some places. The new D304's are documented for tracks in
x05, but we already supported those on read.

They do now document the workout protocols, but I'm pretty sure that we
don't want to get into that business beyond the joyous x05 hack I've
already had to implement.

They do now document land symbols 8294 through 8363 and Marine symbols
180 through 193. Plodding through that list and updating our tables and
doc is tedious but not difficult if anyone would like to tackle that.
(I have no idea which models actually support these - it's kind of an
exercise in faith.)

RJL