I do this by adding an inverted version of all glyphs in the upper
range of the pattern memory. This is a big waste of the pattern
space (only one inverted character is needed at once), but it's the
simplest way to proceed. I'll change this if I ever need more
pattern space.
Also, remove _blank. It was wastefully blanking the whole memory.
Only the name table needs to be blanked on initialization.
In VE on the SMS, the first contents line would always be cleared
because of NEWLN being called when the FBUF would spit its last
char. Inconvenient...
I've added a "graphical" mode to the grid subsystem to inhibit this
behavior in a graphical situation such as in VE.
Also, write a more complete Grid documentation.
Because that mode behaves exactly like in a regular TMS9918, a new
driver for TMS9918 has been added in blkfs and SMS' VDP now uses it.
Also, fix broken 5x7 font.
