Update rust/ekore documentation

[felixhekhorn]

As a side effect of #543 we do no longer expose the references for our implementations. However, since we rely 100% on external sources we must do so.

[felixhekhorn]

@AkshatRai07 Please complete the example function and then then propagate it to all the others in the system

[felixhekhorn]

@AkshatRai07 if you have some time maybe you can also look into the <abbr> hack in doc-header.html and see why it does not work for everything (e.g. here |DGLAP| worked once, but not twice)

[AkshatRai07]

One doubt, some functions in ad_ps call the functions in ad_us, so I need to add those refs of ad_us in ad_ps too right?

[felixhekhorn]

One doubt, some functions in ad_ps call the functions in ad_us, so I need to add those refs of ad_us in ad_ps too right?

ehm ... good question, but I would say no, no need to add them. I'd say the first reference is good enough and people can from there find the dependencies ... in this particular case the dependencies are known since a long time and they don't deserve special attention. In other context this can be a more complicated questions however ... (I can tell you the story at some point in person 🙈 )

[AkshatRai07]

Should we also write the relevant refs for Cache in harmonics? They are there in g_functions and polygamma