Allow for custom block materials

Based on the changes made in shama/voxel-texture#4, this enables
two additional parameters for the game constructor: `materialType`
and `materialParams`, which allow you to specify the default
materials to use and alter their behaviour.
Updating README
More readme clarification
whee typos
Merge pull request #17 from dariusk/master

Cleaning up the README
Merge pull request #16 from hughsk/custom-materials

Custom block materials
fix some physics side effects
Merge branch 'master' of github.com:maxogden/voxel-engine
Given the new physics settings that make it so jump height is no longer variable, we need a bigger jump height in this demo so you can clear blocks.
Merge pull request #18 from dariusk/master

More jump for the demo
use new jump command
Merge branch 'master' into gh-pages
demo