tools/fix: List protocols in usage message

Make fix_client and fix_server more user-friendly by listing supported
protocols in the usage message.

Signed-off-by: Pekka Enberg <penberg@iki.fi>
tools/fix: Configurable SenderCompID and TargetCompID

Make SenderCompID and TargetCompID configurable with the "-s" and "-t"
command line options.

Signed-off-by: Pekka Enberg <penberg@iki.fi>