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/travis_docs.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+
+source util/travis_push.sh
+
+if [[ "$TRAVIS_COMMIT_MESSAGE" != *"[skip docs]"* ]] ; then 
+	if git diff --name-only ${TRAVIS_COMMIT_RANGE} | grep -e '^quantum/' -e '^tmk_core/' -e '^docs/api_.*'; then
+		echo "Generating API docs..."
+		rm -rf doxygen
+		doxygen Doxyfile
+		moxygen -a -g -o -q docs/api_%s.md doxygen/xml
+		git add docs/api_*
+		git commit -m'autogenerated api docs for ${TRAVIS_COMMIT_RANGE}' || true
+	fi
+fi