Provide helptext which was sometimes missing; update some of it
to be more accurate.

Usage syntax messages have the same EBNF as the User's Guide;
there should be no angle brackets in either place.

Don't use "&function"; functions are like arrays, their address
is their name.  Shrink some overlong lines, remove some empties.

Add a couple comments about things that should change:  those
extra TCK cycles for MEM-AP reads are in the wrong place (that
might explain some problems we've seen); the DAP command tables
should be shared, not copied.

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