Using specialized and inline-able parsers instead of strtoul() improved
pixel throughput from ~63MB/s to ~83MB/s (+30%) on a single core
on my machine.
As a side effect, the PX command now allows any non-decimal
character as separator between parameters ¯\_(ツ)_/¯
The canvas_get_size function now returns the number of visible pixels after scaling.
The canvas resize callback now fires after a window was created or updated.
