drag	pan map, including cells
shift-drag	move cell grid relative to map
option-drag	rotate cell grid about map centre
mouse wheel	zoom map, including cells
shift-mouse wheel	zoom cells relative to map (sizes 0 to 8)
space	hide/unhide map
escape	temporarily hide cells (while pressed)
E	hide/unhide empty cells
S or H	square/hexagonal cells
0 to 8	set number of web workers (default=8)