Update to MTL4 formula.

- Download version 4.0.9411 (previous vesion no longer available)
- Add boost dependency
- Update home page (more informative than former home page).

Note: Strictly speaking, Boost isn't a requirement to *build* MTL (MTL is a header library) but it is required to build applications that rely on MTL. Boost is listed as a requirement in the [official building instructions](http://www.simunova.com/node/189) (under "Install a Downloaded Archive").