XPT2046_Calibrated

XPT2046_Touchscreen-based library with 3-point calibration. Based on Paul Stoffregen's XPT2046_Touchscreen library. Adds 3-point calibration support based on a paper by Fang & Chang (Texas Instruments): http://www.ti.com/lit/an/slyt277/slyt277.pdf. See examples for usage.