Implemented first version of parametric flux

Hi Tim,

his is a first stab at my "stage0", i.e. just flux. There are some things that maybe we should be talking about:
- do we like the directory structure I've used?
- there is a `setup.sh` that should give you correct `$PISA, $PYTHONPATH and $BIN`. Does it work on your machine?
- `utils.json` is a bunch of stuff to write/read numpy arrays directly to json. This will convert *every* JSON array into a numpy array. Advantage is that this is still vanilla JSON, downside is speed and flexibility.
- `utils.utils` is a bunch of stuff for dealing with bins, etc. 
- Do we like the way parameters are handled?

I am also happy to receive any other parameters on the code, of course.... Right now I am also not dealing with any of the systematics.