More framebuf functions + better docs.

• Add support for more framebuf methods. Thanks to @raidancampbell!
• Improve lint and docs. Thanks @mrmcwethy !

To use in CircuitPython, download the .zip file and copy its contents to the lib folder on the CIRCUITPY drive. Or, simply install the Adafruit CircuitPython bundle.

Read the docs for info on how to use it.