This changes a number of things in displayio:
* Introduces BuiltinFont and Glyph so the built in font can be used by libraries. For boards with
a font it is available as board.TERMINAL_FONT. Fixes#1172
* Remove _load_row from Bitmap in favor of bitmap[] access. Index can be x/y tuple or overall index. Fixes#1191
* Add width and height properties to Bitmap.
* Add insert and [] access to Group. Fixes#1518
* Add index param to pop on Group.
* Terminal no longer takes unicode character info. It takes a BuiltinFont instead.
* Fix Terminal's handling of [###D vt100 commands used when up arrowing into repl history.
* Add x and y positions to Group plus scale as well.
* Add bitmap accessor for BuiltinFont
Also, renamed Sprite's palette to pixel_shader so it can be
anything that produces colors based on values (including color values).
Added a ColorConverter that converts RGB888 (found in bitmaps) to
RGB565 for the display.
Fixes#1182
It's designed to minimize RAM footprint by using Sprites to
represent objects on the screen. The object model also facilitates
partial screen updating which reduces the bandwidth needed to display.
This is all handled in C. Python simply manipulates the objects with
the ability to synchronize to frame timing.
