fix: use one mask canvas for applying

[KatherineWinter]

Use one mask to apply background color and transparent areas. Downside,
gradients cannot be used as background color.

[timdream]

We will need to move createMaskCanvas.js somewhere outside of src since it is part of the demo, not the library. Perhaps assets? Please also move index.js to that directory too.

I didn't look into the function too much, but thanks for the contribution!

[KatherineWinter]

Bu

We will need to move createMaskCanvas.js somewhere outside of src since it is part of the demo, not the library. Perhaps assets? Please also move index.js to that directory too.

I didn't look into the function too much, but thanks for the contribution!

I would like to make it part of the library, I'll move stuff around

[timdream]

I would like to make it part of the library, I'll move stuff around

I would like to keep the demo and the library separate :)