NEWS: prepare for 6.7.6
Device/Port: remove the "receive timeout" from API docs

The "receive timeout" has been obsoleted by the new method WaitRead().
Device/Port: move code to WaitAndRead()

Eliminate duplicate (and fragile) driver code.  Making the return
value unsigned (i.e. size_t), the API is somewhat more robust.
Device/Port: add a more complex FullRead() overload
Driver/LX: relax download timeout

Allow a memory section download to take up to 5 minutes.  The old
timeout was just one minute, which was not enough for long flights on
4800 baud.