Batgrl

BrailleVideoPlayer` widget plays videos in mono-chrome or optional grayscale with braille unicode characters.

Bug Fixes
----------
Sporadic mouse input on Windows could break the mouse input handler. It's now robust against this.
Terminal resize events on Linux were cleared before being processed. Oops.
`Backspace` ansi wasn't correctly mapped on WSL.

Focusing on add prevents other focusables from being added to `__focus_widgets` when they are being added to the tree simultaneously.

Sprite` helper class removed. This class was made to help with reading, resizing, and compositing textures. Three
functions have been added: `read_texture`, `resize_texture`, and `composite` to replace `Sprite`.

`RaySprites` from the raycaster module have now reclaimed their original name, `Sprite`.

Horizontal and vertical split layout widgets had their names swapped. This is now fixed. Also, `HSplitLayout`'s handle is thinned to match `VSplitLayout`'s handle.

ColorPair.reversed()` returns a new `ColorPair` with the foreground and background colors reversed.

Animation no longer skips last frame.

Two text input widgets added: TextPad for multi-line editable text and Textbox for single-line editable text.

Remove setup.py and setup.cfg and instead use pyproject.toml.