Added support for creating all types of breakable blocks.
Merge from upstream.

Merge branch 'master' into blocks
keys 1 - 0, not 0 - 9
How to play instructions in README

Key bindings and mouse actions
Merge pull request #18 from RichVel/master

"How to play" instructions in README
Update README.md
Merge pull request #1 from fogleman/master

Merge from upstream