Added new function that sketch can call to convert raw ADC x and y
values to calibrated screen coordinates:
tft.convertRawXY(&x, &y);
Redunced required number of SPI transfers needed to read raw values.
Changed mode so PENIRQ pin is enabled so users sketch can read this
signal (if needed).
See issue #279.
Tested on an ESP32 with ST7789V display
SDA read is very slow on an ESP8266 (to be investigated)
Added new setup #define TFT_SDA_READ
Add new ESP32 and ESP8266 compatible in example/Generic folder to test
capture of TFT screen
Bodmer