Add examples of every type of L-function of degree ≤4

[AurelPage]

From /roadmap: Examples of every type of L-function of degree ≤4.

[jvoight]

@davidfarmer How close is this to being done? I don't know any theorems about what "every type" means, and we certainly have some samples in there.

[davidfarmer]

In November, Ralf Schmidt and Dave Roberts described to Sally, Stefan,
and me the complete list of all possible degree 4 L-functions.

There are several types we have not found examples of yet.
It is a research problem to make those examples.

[jvoight]

That's really cool! Yes, if you take your L-functions to come from automorphic representations, then you can make a list of candidates! I think this would be a great project ("feature request"), to collect these examples.

[davidfarmer]

Will be handled by #6236