Adds Proton C Conversion (#4661)

* adds proton c base

* fixes custom matrix include

* adds readme.md

* initial proton coversion, no pin mapping

* start of mcu selection

* add pin mapping and sweet16 test

* add at90 to list

* disable backlight, fix d7

* update flag names

* doc updates

* proton c update for mcu selection

docs/index.html

@@ -17,7 +17,7 @@
       name: 'QMK Firmware',
       nameLink: 'https://qmk.fm/',
       repo: 'qmk/qmk_firmware',
-      loadSidebar: true,
+      loadSidebar: '_summary.md',
       auto2top: true,
       formatUpdated: '{YYYY}/{MM}/{DD} {HH}:{mm}',
       search: {