Add flooding

[ibell]

In FloodState, you should almost never be calling PropsSI, you should always try to call self.pAS.keyed_output instead

[ibell]

You need to implement all the methods of the base class - get_T, get_p, etc. You'll notice that in the pdsim code, we call the get_T, get_rho.. methods in order to not need to pass at all into the python layer. If you don't implement these functions, it will call the base class function, which is not what you want at all.

[ibell]

You should try to get your code to compile now. You will need to add your file in setup.py (in the list of pyx files).