Add bgr and invert options

[RetiredWizard]

Fixes adafruit/circuitpython#9151

This adds the logic from the st7795r library to add an option for switching the colorspace to BGR as well as inverting the display.

[RetiredWizard]

I just noticed #26, I think it would be a simple matter to add a third variable here perhaps called madctl which if passed would be used as the madctl bits and should allow anyone that knows what they're doing to set the rotation/BGR/scrolling values anyway they like. I'm thinking passing in a madctl value would cause the new bgr variable to be ignored.

If you think that's a good idea, I'll go ahead an update this with that change.

[FoamyGuy]

Thank you @RetiredWizard!

I pushed one commit to get the docs to be able to build. recent displayio API changes were causing that to fail, other driver libraries have it in the mock'd list any how. Once everything has shaken out and is matching in blinka displayio, I think perhaps we could use that during the docs build in order to not need for the mocked module.

This looks good to me. I tested it successfully with a Feather M4 + TFT Shield, I was able to use both bgr and invert arguments successfully.

With regards to the optional madctl functionality for more fine grained control. That sounds like a nice feature to me. I don't know if there are any other display driver libraries with that kind of argument, if so we should definitely adopt the same naming convention and API. Feel free to submit a new PR with that feature if it's something you're interested in working on.