General enhancements

• Add: Line element (gslc_ElemCreateLine)
• Add: Support for capacitive touch (FT6206) on Arduino (DRV_TOUCH_ADA_FT6206)
• Add: Support for touch axis swap and flipping on Arduino (ADATOUCH_SWAP_XY, ADATOUCH_FLIP_X, ADATOUCH_FLIP_Y)
• Add: Support for gauge element direction flipping (gslc_ElemXGaugeSetFlip) and improved redraw. Fixed vertical gauge default orientation.
• Add: Support for GUIslice with LINUX mouse support in DRV_DISP_SDL* (eg. Raspberry Pi with HDMI display) using DRV_SDL_MOUSE_SHOW.
• Update: Configuration (GUIslice_config.h) updated to use more consistent notation with #define.
• Add: Added GUIslice config guide (docs/GUIslice_config_guide.xlsx) to demonstrate example CPU / board / display configuration settings.
• Fix: Fixed error in DRV_TOUCH_SDL mode
• Migration Notes (from 0.8.3):
  • The following #define should now use an explicit value (1 to enable, 0 to disable): ADAGFX_SPI_HW, ADATOUCH_I2C_HW, ADATOUCH_SPI_HW, ADATOUCH_SPI_SW, DRV_SDL_FIX_START.