put some default values in screen ram buffer to help work out where
the display jitter comes from.
remove deprecated coregen generated screen ram buffer (using our
own version now).
exise old screen_ram_buffer.vhd from ISE project
adjust VIC to CPU/IO clock ratios and use whole ns units so that
debug output isn't in ps.
debug output to show when screen ram buffer address is adjusted.
add extra wait state when reading character data for character
generator, and debug output used to discover the problem.
fix royally stupid bug caused by updating some signals on the wrong
clock.
fix out-by-one error when reading screen ram buffer