SSD1306 SPI (!I2C) Display

[poevoid]

It'd be really nice to be able to set some defines in the code to switch between an SPI or I2c display for your needs. The SPI display is also able to refresh faster, which might make up the speed difference talked about in the README.md, and would allow for porting to more systems that might have all of these components implemented already, but use the SPI configuration of the SSD1306 display instead of i2c.