I2c buffer sleepwake fix

[FoamyGuy]

@ladyada

Resolves: #137. This implements the changes suggested in #138 as I understand them.

I tested this version successfully with the SSD1306 and confirmed that the sleep/wake are working as expected using the reproducer from here: adafruit/Adafruit_CircuitPython_DisplayIO_SSD1306#47

I also tested simpletest and a few variations of it to ensure the display is initializing and drawing correctly and everything appears to behave normally to me.

Should also resolve:

• sleep() and wake() throw errors on Blinka Adafruit_CircuitPython_DisplayIO_SSD1306#47
• Return of the wake/sleep issue Adafruit_CircuitPython_DisplayIO_SH1106#21 (The only SSH1106 I have is on the macropad and I don't know if possible / how to test it with RPi.)

Also removed the get_html_theme() call from the docs config which is deprecated and how raises an error when building the docs.