doc: not all debug adapters are "dongles"

doc: not all debug adapters are "dongles"

Talk more about "debug adapters" instead of only "dongles".  Not all
adapters are discrete widgets; some are integrated onto boards.  If
we only talk about "dongles" we rule out many valid setups, and help
confuse some users (who may be using Dongle-free environments).

Also start bringing out the point that JTAG isn't the only transport
protocol, even though OpenOCD historically presumes "all is JTAG".
(Not all debug adapters are JTAG adapters, or JTAG-only adapters.)

Plus a few minor fixes (spelling etc) in the vicinity of those changes,
and updates about FT2232H clocking issues (they can go faster than the
older chips, and can support adaptive clocking).

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>