Francesco Adamo / Mbed 2 deprecated SSD1306_demo

- code cleaned up in many points for a better readability - removed SPIPreinit and I2CPreinit classes - moved various method implementations from .h files to the corresponding .cpp ones - the splash() and clearDisplay() methods now directly update the display; no more need to call the display() method after them

Dependencies:   Adafruit_GFX mbed

Fork of Adafruit_GFX by Neal Horman