Public docs for Window

[Starbuck5]

For #2603

This moves the docs for Window from sdl2_video.rst to a new window.rst. I've declined to categorize it, so the new module docs shows up in the "other" category on the module index at the top of the documentation.

I also added the following blurb to the Window class description:

The Window class (formerly known as _sdl2.video.Window), is a newly published feature of pygame-ce 2.4.0. This class allows for programs to drive multiple Windows on-screen at once, something not possible with the pygame.display.set_mode() API. Not everything possible with pygame.display is possible yet in the Window API, but the new window class will continue to be developed, and we're excited to share the new functionality this class offers.

[Starbuck5]

I'm not sure why the linux circle ci is failing, this is a docs PR, the failure must be unrelated.

[MyreMylar]

LGTM 👍

[ankith26]

Generated the docs locally, and while Window does show up in the top bar in the base index.html, it does not show up when focused on the docs for any other submodule

[Starbuck5]

Try running a full regen.

[ankith26]

LGTM, thanks for the PR 😎