Usability Test improvements

Updated indestructible block grow function (which was terribly
outdated), allowing enemies to be pushed and destroyed by creating
blocks off of them.

Improved instructions:
-Added alternate controls
-Mentioned purpose of number in top left
-Mentions enemy pushing/squishing

Raised the death plane to reduce time spent falling before death

Made enemies knock the player away from them.  The player can get into
some bad spots now!