EC - check of peak energy

[jsitarek]

In https://github.com/jsitarek/agnpy/blob/master/tests/basic/simple_ec.ipynb I put a few tests of the EC code comparing it with back of the envelope calculations.

in [15] (test2) compares the peak energy of the EC spectrum for Thomson case without beaming, there is a factor of 3.3 difference here, out of which I can understand a factor of 2

in [22] (test3) there is the same check done in K-N regime (still without beaming), here the values match (but they are also limitted by a somewhat different process)

in [26] (test4) the same is done for Thomson regime but with strong beaming, the difference is smaller in this case ~ 1.3, maybe good enough?

[cosimoNigro]

Can we close this? It's been a while since we get a good agreement for all the EC cases...

[jsitarek]

I updated the old notebook in PR #94 reruning it with the current code.
The old differences in photon density are gone now.
In this notebook there was a check of peak positions in which there was a difference of a factor of 3.3 w.r.t. theoretical calculations for the case of nearly stationary blob - out of this factor I could explain a factor of 2.
For the fast moving blob the agreement was much better (a factor of 1.3).
I think all the tests comparing with the literature were also done for the case of fast blob, and this is also a main use case of the code. We might want to introduce some check or a warning if somebody tries to put a non-relativistic blob, but except of this I think the issue can be closed.