Easy multicolor support

[TheMisfit68]

Found an excellent idea online
to get a neumorphic design compatible with all kind of color schemes,
but without having to provide color-assets or custom shadows for each color used:

The default dark and light shadows are just black and white and get blended onto the design

`.shadow(color: .white, radius: 15, x: -10, y: -10)

.shadow(color: .black, radius: 15, x: 10, y: 10)

.blendMode(.overlay)`

This could greatly simplify the implementation as the project supports more and more controls.

Just an interesting idea

[costachung]

This is a good idea for people who want to use neumorphic UI on different color backgrounds (except black and white) without having to pick which color to use for the shadows.

That looks like an optional feature from the API-level point of view.

First, We have to test the blend mode to see if this work on both "inner" and "outer" shadow.

Second, I need to think about where to add this in the API. And we can discuss about it later.

That's an interesting topic. Let's keep this open.