Simplify sample.

As I read up on low level disk writes, I realized that my data run
aligmnent code was overkill.  This commit reduces the data run
handling code to a RTS instruction and the sync run code just
flags the self sync bytes as $7F (which never occurs in nibble values
read from disk since they must start with the high bit set.)  The
low level writing code will detect these $7F bytes, flip the high bit
back on, and then add 8 more clocks of delay after the write to create
the self sync byte on disk.