Added Physics js and some scratch code using it.
Added .gitignore file, ignoring Emacs backup files.
Finished up a simple demo of moving and jumping.
Merge branch 'master' into physicsjs
Got a very basic prototype working with the new physics engine. Not
integerated with the older code yet, though.
Got rid of unused "fixed" option.
Added an extra platform to my demo "game".
Merge branch 'master' into physicsjs
Moved _.js to a CDN and added jQuery.
Fixed image scaling and added zombie platforms.
Got the skeleton of the first level going.
Merge branch 'master' into physicsjs
Merge branch 'master' into physicsjs
Fixed how the base world is set.
Implemented DEATH
Fixed image widths.
Renamed player-old.js to its original name.
Fixed a couple of bugs with the controls.

  - left and right should not interfere with each other too much
  - pressing up in the air doesn't cause you to jump after you've landed
this.image => this
Support multiple levels.