The buffer's implementation wasn't buying us much in exchange for its
complexity. A modern machine was still too fast for it (copy/pasting
text from a modern machine would send bytes too fast for the RC2014)
and in the (theoretical so far) case of COS-to-COS communication, the
buffer didn't help in cases where the baud rate was faster than the
processing of each byte received (for example, if the byte was written
directly to EEPROM).
I'm scrapping it and, instead, use the RTS flag to signal the other
side when we're ready to receive a new byte.
Also, implement driver for channel B in SIO. I will need it to talk
to my TRS-80 4P.
Working in "blk/" folder from a modern system is harder than it
should be. Moving blocks around is a bit awkward, grepping is a
bit less convenient than it could be, git blame has troubles
following, etc.
In this commit, we modify blkpack and blkunpack to work with single
text files with blocks being separated by a special markup.
I think this will make the code significantly more convenient to
work into.
