Emulate new FPGA Blink Screen dimension registers

SCW ($70, Screen width in multiple of 8 bits) SCH ($71, Screen height in multiple of 8 bits)

OZvm will implement a new Z88 -> "Screen Resolution" menu item which will hold a sub-menu of available resolutions:

(characters are defined by a 6x8 pixel square)

• 640x64 (106x8 characters, default)

• 640x256 (106x32 characters)

• 640x480 (106x60 characters)

• 800x256 (133x32 characters)

• 800x480 (133x60 characters)

OZvm will render the screen pixel matrix, according to selected resolution.