feat: canvas scaling for "high quality" output

[WUGqnwvMQPzl]

Adding canvas scaling option for someone doesn't satisfied with 250p output and someone using HiDPI screen.

Also hard-coded max width of the canvas element so scaling won't messing up the layout.

Side note: Be better to use SVG instead of PNG for halo and cross texture, there's another PR already doing that: #6

Preview

Default 1x output:

2x output: