Squashed 'vendor/arduino-makefile/' content from commit 73f08aa

git-subtree-dir: vendor/arduino-makefile
git-subtree-split: 73f08aad76fc01efa80c80aa7ff2bf328ad34cee
Merge commit '720ae064a46ae64e8b1502acf40fe2e7ea776b74' as 'vendor/arduino-makefile'
Add test sketch using arduino-makefile to build
Add documentation