Some premature optimization ;-)

Moved the call to video_spi_wait before the writes.
Otherwise SPI would not operate asynchronously at all.
Minor syntax changes.

OR A, C is more readable than just OR C
Monitor needs the latest changes from the video branch: changed order of spi wait and write

Merge branch 'video' into monitor
added .video_spi_write_A shortcut to directly send the value in A to the video device
Merge branch 'video' into monitor

monitor needs the latest video interface (again) for directly writing values from A to the video device
machine code monitor now shows a hexdump :)

* Makefile: added new files
* hexdigits.asm: XREFs before XDEFs for consistency
* linechars.asm: new file, implements solid square characters
* main.asm: removed test code, jump into monitor
* monitor.asm: new file, implemented hex listing
* video.asm: some XDEFs, changed default background color