Api extras

[hyanwong]

Make tsdate.date() a wrapper for tsdate.inside_outside(), tsdate.variational_gamma(), or tsdate.maximization(). This allows easier documentation and reuse, and is a follow-up to #350

Also ban tsdate.maximization() from using the return_posteriors parameter.

[nspope]

LGTM -- this'll break #349 but it should be easy enough to fix. I worry a little bit about tying the output to a Results class, because I think we may want to return different things from different methods ultimately (for example, the variational gamma method gives a per-edge "likelihood" that could be useful, and I'm not sure there's an analogue for inside-outside). But, if it comes to that I suppose we can make method-specific Results classes that at a minimum contain the 4 fields in the base case.

[nspope]

Also need to update numba version in setup.cfg, looks like pip prioritizes this

[nspope]

also what do you think about splitting the contents of core.py into different files? It's getting a bit big, what with the API, the algorithms, and the likelihood objects?

We don't have to do that now though (it'd be better to wait until the conflicts with #349 are resolved)

[hyanwong]

Thanks so much for looking at this @nspope. Re the "results" class, this is an internal thing that is never exposed to the user (it's just to make out lives easier), so we can rework it later however we like.

I agree about splitting up core.py, which we can do later. It may also be that we can place some of the gamma stuff within the VariationalGammaMethod class?