Release v0.16.0

This release is a major roll-up of many incremental enhancements.
Note that the Builder is separately downloaded from the GUIslice-Builder repo

Changes since 0.15.0:

• Enhance: Utilize fast TFT_eSPI clip / viewport rendering (#274)
• Enhance: Major updates for XKeypad (#255), support of custom keyapds.
• Add: Support for PlatformIO
• Add: transparency in image draw from RAM (#253)
• Add: new configs (LCDGFX #248, ILI9226, SDL2)
• Change: Removed GUIslice_config_ard/linux.h
• Fix: transparent text (#273)
• Fix: pgmspace compatibility (#248)
• Fix: compiler warnings (#248,
• Fix: toggle button rounded corners, swap left/right (#271)
• Fix: GFX font offset (#277)
• Fix: XGraph math ranges (#285)
• Fix: GSLC_LOCAL_STR mode

Migration Notes:

• Changes to the XKeyPad API may require updates to existing sketches that utilize the widget. Please refer to the XKeyPad Migration Notes for details.