Acceleration

[TobiasWinchen]

Implementation of first and second order Fermi acceleration.

The code is documented in the new notebooks in the doc directory:
https://github.com/TobiasWinchen/CRPropa3/blob/acceleration/doc/pages/example_notebooks/acceleration

While integrating the examples I slightly restructured and streamlined the existing documentation.

[TobiasWinchen]

Thanks for your comments, I updated the spelling + coding style accordingly.

[adundovi]

Hi Tobi, it is OK from my side. However, I checked it on a technical level only, not equations and physics, yet I assume you test this carefully.

[rafaelab]

I am still testing this. I will merge the PR once I'm done (probably early next week).
I'm just concerned that some combinations of energy losses and energy gains might mess things up, so I'm testing some limiting cases. I haven't found anything so far.
Btw, great work, @TobiasWinchen !

[rafaelab]

@TobiasWinchen I have finished reviewing the PR and testing the module. I have no more comments.
Let's just wait until 3.1.7 is released on Friday, and then we can merge your PR, since this is a feature of 3.2.

[rafaelab]

Ready to be merged.
@TobiasWinchen : just make sure to add the relevant information to the Change Log before merging.