Adding TWKB format

TWKB format is a compressed binary format. 

It is new and a moving target but is in the PostGIS trunk.

The code is passing all testes, but it is not very well tested yet with different geometry types and so on.

I have tried to follow the style of other code in the project but I am not a JavaScript guy so bare with some ugliness.

I will fix it when you point at it.