Modifications to setup script

Hi there, I made a few changes to the setup script.

Firstly, I made a call to the system so that extract_camb.sh is run through the setup script (rather than having to run it yourself first). This makes it more like a normal python package to install.

Secondly I added the ability to use "extra_f90_compile_args" with versions of numpy > 1.6.1. I had some trouble with this previously. With later versions, this argument provides the f90 arguments, while it seems that the previous "extra_compile_args" doesn't really do much at all. Not sure why. But this seems to work now.

Cheers,
Let me know if there's something that doesn't work.