Update links, README, contributing, etc.

.github/FUNDING.yml

.github/contributing.md

.github/issue_template.md

Marlin/Configuration.h

Marlin/Marlin.ino

Marlin/src/HAL/AVR/fastio.h

Marlin/src/HAL/DUE/Tone.cpp

Marlin/src/HAL/DUE/fastio.h

Marlin/src/HAL/DUE/usb/arduino_due_x.h

Marlin/src/HAL/DUE/usb/compiler.h

Marlin/src/HAL/DUE/usb/conf_access.h

Marlin/src/HAL/DUE/usb/conf_clock.h

Marlin/src/HAL/DUE/usb/conf_usb.h

Marlin/src/HAL/DUE/usb/ctrl_access.c

Marlin/src/HAL/DUE/usb/ctrl_access.h

Marlin/src/HAL/DUE/usb/genclk.h

Marlin/src/HAL/DUE/usb/mrepeat.h

Marlin/src/HAL/DUE/usb/osc.h

Marlin/src/HAL/DUE/usb/pll.h

Marlin/src/HAL/DUE/usb/preprocessor.h