Added BoundsOverlay Rendermode Primitive

[jpchip]

As a response to #1332 and designed to Display land ownership on map.bitquest.co, I created a new RenderMode Primitive called BoundsOverlay. This rendermode overlays colors on the map within sets of bounding boxes, specified as multiple tuples of the form (minx, minz, maxx, maxz). So by specifying (0, 0, 16, 16) all the blocks (inclusive) within the boundary created by these coordinates will be colored. The color is specified as (r, g, b, a).

An example usage in the config.py would be:

renders["boundsoverlay"] = {
        'world': 'woot',
        'title': 'Land Ownership',
        'rendermode': [ClearBase(), BoundsOverlay(bounds=[
                        (((0, 0, 16, 16), (-70, -30, -54, -14)), (255, 160, 122, 127)),
                        (((100, 100, 116, 116),(17, 0, 33, 16)), (75, 0, 130, 127)),
                       ])],
        'overlay': ['day']
}

with a result like:

I also updated the docs with example usage.

[gluth]

Overall: there is nothing critical here, but few changes need to be applied to increase code readability and overall code quality.

[gluth]

Code format need more care here and over the whole PR.

[gluth]

This if is taking whole function with exception for one command at the end. I would invert it and close function fast. By example:

if (!opt || opt == Py_None) {
  self->parent.get_color = get_color;
  return 0;
}

There is one line which will be repeated, but overall this will increase code readability with limited number of levels.

[gluth]

Similar situation here, if not cond set parent color and return 0. There is no need to wait with this till the function end.

[gluth]

The same condition in two ifs side by side, join them into one if or fail fast if there is no self->bounds.