Add support for scripts to delimiters

[gsomix]

Fix for #62

cc @illiteratePhD

[alexreg]

Looks good to me.

Just a random thought: once we overhaul the parser (perhaps using what I wrote for MathTex.NET), we can add automatic \left and \rightto brackets/delimiter symbols.

[ForNeVeR]

@alexreg I think that'll contradict the default LaTeX behavior. While I can clearly see why it's useful, I'm not sure we need to introduce such behavior. Although we can make it optional.

@gsomix thanks for the contribution, that's very nice.