Attiny85-vga UART receiver goes into command-mode whenever
"Escape" 0x1B (ascii 27 / ESC) character is encountered. Sending multiple ESC
characters consecutively has same effect as sending just one.

2nd byte			command
===========================================
bits	7..5	4..0

	000	<command>	Basic command-set, where <command> is:
				1:	Clear screen and move
					cursor to 0,0.
				27:	command-mode (ESC)

	001	<X>		Move cursor X-coordinate to <X> 
				(0..31). Y-coordinate unaffected.

	010	<Y>		Move cursor Y-coordinate to <Y>
				(0..13). X-coordinate unaffected

	011	<ext>		Extended command-set, where <ext> is:
				1:	Wrap-around mode.
					Screen will not scroll, enter 
					(13) will not advance
					to next line, but prints ascii
					code 13 instead.
				2:	Scroll-mode. Screen will scroll
					up when text overflows from last
					line. Enter (13) moves cursor to
					beginning of next line.

	101	<line>		Clear line number <line> (0..13), cursor is not
				moved.

	110	<color>		Change color to <color>. Color will stay selected
				until it is changed again. Clear screen -command
				resets the color back to default.

	111	ignored		Reserved for future

Add spec-draft of UART commands to be implemented
Add spec-draft of UART commands to be implemented
