Use options objects to set properties on World, Body, and Spring.

This allows for a very nice way to set every property on an object if
desired.
Merge pull request #3 from Fishrock123/master

Lets get some grunt building in here!
Merge pull request #7 from Fishrock123/options

Use options objects to set properties on World, Body, and Spring.
Merge pull request #8 from Fishrock123/master

Remove p2.js from the root directory.