Merge pull request #6 from pounard/master

Deambiguates VariableDeclaration and VariableReference
Merge pull request #7 from pounard/master

Make the grammar work with my existing real life leek scripts
Merge pull request #8 from pounard/master

Added prefix ++ and -- expression and statement
Added For, ForIn, PrefixIncrement, PostFixIncrement, PrefixDecrement, PrefixDecrement tests.