Update to 0.53 with feature fixes

Many things learned in the last week, and applied here:

- a really cheap cosmetic trick: if your browser supports it, Piko will
try resizing your window to something closer to the actual device size.
TODO: let the user choose a new device size easily.

- made checkers for PhoneGap and Android, because those are always
handy to have around. TODO: make the Android check turn into a more
versatile device check.

- added <container> to the body of the index.html file. There was an
instance where the viewport was scrolling without permission. The
container prevents that. It's a stupid hack, but those are usually the
best hacks, so hey.

- added sound support, for an app I was working on. Requires the media
plugin for Cordova, but it lets you start sounds easily, and
theoretically loop them. TODO: add proper documentation, and fix a
possible gap in the audio looping.

- appInit() added, for things that need to happen as soon as the app
starts up, but before it actually works.

- killing the splash screen, if it exists (not usually necessary, but
for some apps, very vital)