Generate API docs from source code comments (#2491)

* Generate api docs from source code

* Add a bunch of doxygen comments

* more doxygen comments

* Add the in-progress api docs

* script to generate docs from travis

* Add doc generation to the travis job

* make travis_docs.sh commit the work it does

* make sure the docs script exits cleanly

util/generate_api_docs.sh

@@ -0,0 +1,31 @@
+#!/bin/bash
+
+set -x
+
+if ! doxygen -v 2>&1 > /dev/null; then
+	echo "doxygen not found! Please install it!"
+	exit 1
+elif ! moxygen -V 2>&1 > /dev/null; then
+	echo -n "moxygen not found! Would you like to install it? [y/n] "
+	read ANSWER
+	case $ANSWER in
+		y|Y|yes|YES|Yes)
+			npm install -g moxygen
+		;;
+		*)
+			exit 1
+		;;
+	esac
+fi
+
+if [ ! -e Doxyfile ]; then
+	echo "Error: You must run this from the top-level qmk_firmware directory!"
+	exit 1
+fi
+
+# Generate the doxygen XML files
+rm -rf doxygen
+doxygen Doxyfile
+
+# Generate the moxygen Markdown files
+moxygen -a -g -o docs/api_%s.md doxygen/xml