Release of version 2.2.0

What's Changed

• added section to README about the LED pin as input issue by @boramonideep in #228
• Sync develop with master (V2.x) by @boramonideep in #230
• Changes in boards.txt for V2.x by @boramonideep in #231
• Refactored built-in libraries by @boramonideep in #235
• V2.x LED Library reversed LED_BUILTIN by @techpaul in #233
• added changes to enable PWM channel in XMC1100 Boot Kit by @boramonideep in #239
• Variable gain ADC feature by @boramonideep in #240
• GPIO Init after USIC CH Start by @9Volts9er in #238
• Develop by @jaenrig-ifx in #248

Full Changelog: V2.1.0...v2.2.0