add docs example for pathfinder

[mitzimorris]

Summary:

Add example notebook for Pathfinder to docs.

[mitzimorris]

the output from running Pathfinder (or something it calls) is a tad confusing - one run of multi-path Pathfinder runs 4 chains, but console message looks like it only ran one chain - change wording?

update: message is coming from here:

cmdstanpy/cmdstanpy/model.py

Lines 2036 to 2040 in 2cf6120

	logger_prefix = 'CmdStan'
	console_prefix = ''
	if runset.one_process_per_chain:
	logger_prefix = 'Chain [{}]'.format(runset.chain_ids[idx])
	console_prefix = 'Chain [{}] '.format(runset.chain_ids[idx])

[mitzimorris]

also updating wording in variational notebook example, since there's now 2 variational methods as part of this issue.
noticed that there's links to readthedocs.io instead of mc-stan.org/cmdstanpy. fix everywhere or file a separate issue?

update: Variational notebook only offender. fixed.

[WardBrian]

The "Chain [1]" label comes from

cmdstanpy/cmdstanpy/model.py

Line 2038 in 2cf6120

if runset.one_process_per_chain:

Party of the patchy logic to make our fake multi chain look like the real multiple-chains-single-process

[mitzimorris]

• the User's Guide is stale - needs work.
• we need examples for the Laplace method as well.

[mitzimorris]

@WardBrian - we're planning to do a 1.2 release before doing a 2.0 release, correct?

started work for this issue here: https://github.com/stan-dev/cmdstanpy/tree/docs/701-pathfinder

should I generalize this issue (and rename accordingly) to make this a docs update for everything in 1.2?

[WardBrian]

What else needs updating besides the changelog (already in #691)?

[mitzimorris]

I'm checking the .rst and .ipynb notebooks in folder docsrc/users-guide - I'm not sure they're all up-to-date. do we want to document laplace method in the users guide? it's a very minor feature.

[WardBrian]

I think just the API documentation on laplace is probably sufficient. Of course, more documentation is never a bad thing