INT 10 - VIDEO - AX PC - REGISTER EXTERNAL CHARACTER

	AX = 5100h
	BH = character width in bits (10h)
	BL = character height (10h)
	DX = character code (DH = F0h-F3h, DL=40h-7Eh,80h-FCh)
	ES:BP -> character bitmap
Return: AL = status (00h successful, 01h failed)
SeeAlso: AX=5101h,INT 1F"SYSTEM DATA"