Update on python API to correct undefined references

[jmllorens]

Since the migration to the new C API the python module stop working as expected. A few errors appear after import:

• undefined functions: Layer_Init, Material_Init, Material_InitTensor, Simulation_AddMaterial, Simulation_GetPoyntingFlux and Simulation_MakeExcitationExterior
• The SetFrequency stop detroying previous results.

All these dependencies to the old API have been corrected by upgrading to the new C API when possible.

Old API calls still remains, although the python extension is more useful that the current version.

[kwrobert]

Works like a charm! Thanks so much for making these corrections.

[jmllorens]

@kwrobert After sending the pull request I noticed that some of functions which still use the old API are not working properly. For example, I fixed S4Sim_SetRegionCircle in my fork, because is one of the functions I use most. Probably it is a better a idea to wait until S4v2 is merged with master to implement all the changes.

[Chronum94]

I get a ImportError: /home/chronum/S4/jmllorens/S4/build/lib.linux-x86_64-3.6/S4.cpython-36m-x86_64-linux-gnu.so: undefined symbol: PyInt_AsLong when working with this. Any ideas?