Use go:embed for bundling

[Nv7-GitHub]

This uses Go 1.16's embed package instead of embedding files as []byte.

This has a few benefits:

• This only needs to be run once, not every time an icon changes
• From my testing, it reduces output binary size (although only by ~16kb)
• Bundling is a tiny bit faster (0.026s -> 0.07s)

Overall it doesn't really affect things too much, but I think it is a little bit better.