Add problem matchers for Github actions

- Add a basic problem matcher for illuaminate errors.
 - Add a script (tools/parse-reports.py) which parses the XML reports
   generated by checkstyle and junit, extracts source locations, and
   emits them in a manner which can be consumed by another set of
   matchers.

This should make it a little easier to see problems for folks who just
rely on CI to test things (though also, please don't do this if you can
help it).

config/pre-commit/illuaminate-lint.sh

@@ -5,5 +5,12 @@ test -d bin || mkdir bin
 test -f bin/illuaminate || curl -s -obin/illuaminate https://squiddev.cc/illuaminate/linux-x86-64/illuaminate
 chmod +x bin/illuaminate
 
+if [ -n ${GITHUB_ACTIONS+x} ]; then
+    # Register a problem matcher (see https://github.com/actions/toolkit/blob/master/docs/problem-matchers.md)
+    # for illuaminate.
+    echo "::add-matcher::.github/matchers/illuaminate.json"
+    trap 'echo "::remove-matcher owner=illuaminate::"' EXIT
+fi
+
 ./gradlew luaJavadoc
 bin/illuaminate lint