Compute analytically the radiation integrals

[lfarv]

The 5 radiation integrals are computed analytically by get_radiation_integrals in radiation.py. 2 new functions allow a comparison between results obtained from the radiation integrals (radiation_parameters) and from ohmi_envelope (envelope_parameters).
A slight difference with Matlab in i4 is under investigation

[lfarv]

This is now OK for me. New features:

• a Lattice.circumference property,
• a get_radiation_integrals function / Lattice method to compute the radiation integrals,
• radiation_parameters and envelope_parameters functions and Lattice methods returning an object summarising some lattice properties, such that print(ring.radiation_parameters()) gives a readable summary.

Function names can still be modified if there are better names!

[willrogers]

I'm happy to merge this. I think the tests comparing Matlab and Python results are becoming very useful.

[lfarv]

Ok, @willrogers, go on merging.
You are right, comparison tests are very useful: I could fix a small bug in my formula for I4.
Here the comparison between numerical integration in Matlab (for I4 and I5) and analytical integrals in Python shows a very good agreement.

I see that the correction for NumIntSteps is still in a pending pull request, so I add it here.

I have also a question on the updates of the Pypi repository: when is it updated? Since pyat is still evolving quite fast, I would push for rather frequent updates…

[willrogers]

In principle, if I push a tag pyat-x.y.z, wheels should be built and uploaded to test PyPI. If these work successfully I can then download them and upload them to the real PyPI.

I'm happy to try that now (0.0.2), then when we've merged the Diamond changes I can make a 0.0.3 release.