Add a help target to a Makefile that will allow all targets to be self documenting

Makefile

.SILENT:
.PHONY: help

# Based on https://gist.github.com/prwhite/8168133#comment-1313022

## This help screen
help:
	printf "Available targets\n\n"
	awk '/^[a-zA-Z\-\_0-9]+:/ { \
		helpMessage = match(lastLine, /^## (.*)/); \
		if (helpMessage) { \
			helpCommand = substr($$1, 0, index($$1, ":")-1); \
			helpMessage = substr(lastLine, RSTART + 3, RLENGTH); \
			printf "%-15s %s\n", helpCommand, helpMessage; \
		} \
	} \
	{ lastLine = $$0 }' $(MAKEFILE_LIST)

## Another dummy task
another-dummy-task:
	echo dummy