Add ColorOverlayFilter

[mudcube]

The ColorOverlayFilter replaces all colors within a source graphic with a single color, respecting the alpha channel of the source graphic. See attached graphic for visual example:

[bigtimebuddy]

Great work! There are few other small things that would be useful if you could hit:

• Integrate this into tools/demo
• Generate a screenshot (see tools/screenshots)
• Add to the root README.md
• Add to the bundle README.md

[mudcube]

@bigtimebuddy Is there a way for the demo to only apply the filter to the swimming critters? I added the reference to this filter, but it appears to be applying it to the entire scene, which results in an image with a single color.

[bigtimebuddy]

I think the property is fishOnly. Drop shadow and glow do this for an example.

[mudcube]

It should be all working now!

BTWs, what's the best way to build the current working tree of pixi-filters while in development? Since the source files are checked out from npm, both the demo and the screenshot build utilities appear to not take into account any updates made to the code within pixi-filters without manually cutting/pasting the code you're currently working on into the built Javascript.

[bigtimebuddy]

Running npm run watch at the root-level only handles changes to the filters or bundles themselves. If you want to watch for the demo app, you should cd into tools/demo and run npm run watch. I can work on better ergonomics for this.

[bigtimebuddy]

Great work @mudcube.