allow files with underscore
add google analytics
Merge branch 'master' of https://github.com/rossmckelvie/string-theory into gh-pages

* 'master' of https://github.com/rossmckelvie/string-theory:
  update story and add enemies
restore DOMSound
Merge branch 'gh-pages' of https://github.com/rossmckelvie/string-theory into gh-pages

* 'gh-pages' of https://github.com/rossmckelvie/string-theory:
  add google analytics