Optimization of Serial Data

[Kirb0031]

Regarding MEGA65/m65dbg#3 and serial speed issues.

Current serial output is inefficient (repeats banner every time, includes spaces, etc).
A more efficient, but less human readable, protocol for use with m65dbg was suggested
which should improve debugging performance.

[Ben-401]

maybe improve the existing format by not repeating banner etc, but keep this human-readable-format for users that do not want to use the m65dbg.
the fpga-side serial-debugger could by default use the above human-readible-format, and when it recieves a special message from the m65dbg, the fpga-serial-debugger could switch its format to the optimised one.

[gardners]

This is the general plan: we can implement a command that switches the
mode. That said, I am also comfortable with us making m65dbg a mandatory
tool for using the serial debugger, if it results in significantly improved
utility.