Cleanup.

Use existing functions for converting bytes, i.e. NIBBLES.
Accept IPv6.
Fix sequence handling for WRITE-SEQUENCE.
Start refactoring of functions.
Optimize single byte access.
Extract magic constant.
Fix EOF behaviour, add READ-SEQUENCE.

With this we still can't buffer on the reading side, but it's better
than nothing.
Don't use LOGV.
Use OR instead of UNLESS.
Add a maximum buffer size and honour it.

Needs cleanup, but works fine.
Tests infrastructure.
Fix system definition.
Export main function.
Update USAGE info and move to front.
Export global settings.