Add megaavr / nano_every support, via midasgossye

Author: ianfixes

Diff for: CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Added
 - Working directory is now printed in test runner output
 - Explicitly include `irb` via rubygems
+- `arduino:megaavr` architecture is now included by default, using the `nano_every` platform, via midasgossye
 
 ### Changed
 - Update .gitattributes so we have consistent line endings

Diff for: misc/default.yml

@@ -9,6 +9,8 @@ packages:
     url: https://downloads.arduino.cc/packages/package_index.json
   arduino:samd:
     url: https://downloads.arduino.cc/packages/package_index.json
+  arduino:megaavr:
+    url: https://downloads.arduino.cc/packages/package_index.json
   esp8266:esp8266:
     url: http://arduino.esp8266.com/stable/package_esp8266com_index.json
   adafruit:avr:
@@ -57,6 +59,17 @@ platforms:
         - NUM_SERIAL_PORTS=2
       warnings:
       flags:
+  nano_every:
+    board: arduino:megaavr:nona4809
+    package: arduino:megaavr
+    gcc:
+      features:
+      defines:
+        - MILLIS_USE_TIMERB3
+        - NO_EXTERNAL_I2C_PULLUP
+        - AVR_NANO_4809_328MODE
+      warnings:
+      flags:
   esp32:
     board: esp32:esp32:featheresp32:FlashFreq=80
     package: esp32:esp32