Library did some allocs without free and lots of un-initialized variables.

Applied pull requests from esp8266-oled-ssd1306:

squix78/esp8266-oled-ssd1306#169
squix78/esp8266-oled-ssd1306#157
squix78/esp8266-oled-ssd1306#144

And applied the suggestions from issues:
squix78/esp8266-oled-ssd1306#170
squix78/esp8266-oled-ssd1306#161

Support multiple display resolutions

Applied PR from esp8266-oled-ssd1306:
squix78/esp8266-oled-ssd1306#133

Better Brightness / Contrast control

Suggestions taken from this issue:
squix78/esp8266-oled-ssd1306#134

It is now the same version as being used in ESPeasy.

Fix platforms in library.json

fix typo in integer type (causes compile error)

Closer to middle vertical align

Make OLEDDisplay.display() an abstract function

Implement setLoadingDrawFunction. Fixes #102

Without the `= 0` declaration, compiling with RTTI enabled fails.
See http://stackoverflow.com/a/307427/1880101 for an explanation.

Due to the 4px spacing, the indicators are a bit offset when adding them to LEFT or RIGHT sides of screen

Improve display performance of SH* drivers

Add SH1106Spi support

Fix internal black drawing

Add sample code

Make it possible to enable/disable all indicators

Fix a bug where multiline strings where not correctly centered

Improving rect drawing