First of all, as everybody said: Congrats !
You were the fastest ha ha
... I was planning to make an adventure game engine in html5/js. I had begun collecting resources last year and AGS (that's still my favourite engine) was in my opinion the best candidate to analyse (api requirements ...) for my first experimentations.
I took a look at your js code. Indeed, it's a really incomplete engine but there are nice stuffs all the same (in my case, I wasn't planning to base all on canvas but also on imgs-areas-maps but it seems to rock anyway) !
Just about the music and sounds:
* On mobile safari, there is currently a bug that impede playing more than one sound file at the same time and I don't know when they plan to fix it
* I think when the new mozilla audio api will be popularised and used , it will allow playing more audio formats - a bit like new flash 10 stuffs allow now. And there are already experimentations done about Amiga MODs playing what is really awesome: you might take a look at the dynamicaudio.js library and the jsmodplayer project on github, it's really interesting
Good luck with it all!