Add optional delay between each transmitted byte

Add optional delay between each transmitted byte

The bit-banger seems to be too slow to read a byte
immediately following another at 57600 baud.

Today's fast computers can also be a factor, since the
server code might have incurred some "natural" delay in
the old days.

The previous setting of non-buffered I/O is a prerequisite
for this code delay to make a difference.

A value of 500 (microseconds) works fine on a Dragon 32
using its DLOAD command patched with DriveWire serial
drivers at 57600 baud.

This brings the effective transfer rate down quite a bit from
what 57600 baud could theoretically allow, but it is still around
2KB/s.

Signed-off-by: Tormod Volden <debian.tormod@gmail.com>