Add Plugin base classes APIs to readthedocs

[forslund]

Description

This updates the docstrings for the base classes for the pluggable systems to provide more of the information needed for creating plugins. Plugins are also added to the API documentation.

I'd very much appreciate improvementson the docstrings I've suggested here.

How to test

run make html in the docs folder and check that the resulting plugin documentation looks good.

Contributor license agreement signed?

CLA [ Yes ]

[devops-mycroft]

Voight Kampff Integration Test Succeeded (Results)

[krisgesling]

Hey Ake, this is such a huge improvement, thankyou!!!

A bunch of comments but all little things. Definitely push back if I've misunderstood anything.

[forslund]

I've updated with the suggested texts (in all cases except one) I tried to reword the index page. but might need some more tlc.

[devops-mycroft]

Voight Kampff Integration Test Failed (Results)

[devops-mycroft]

Voight Kampff Integration Test Succeeded (Results)

[krisgesling]

Is there a commit missing here, I'm seeing a few unchanged.

Also small nitpick - we don't seem to be consistent with the argument type being before or after the colon, eg:

some_arg (type): description
some_arg: (type) description

[forslund]

I'll look over the argument type changes. Likely I've gotten confused over time and mix up the order. Can you give an example of unchanged?

[forslund]

Now I see what you mean. I seem to have missed most of your comments. sorry about that

[devops-mycroft]

Voight Kampff Integration Test Succeeded (Results)

[forslund]

I think this is once more ready for review. All of the comments should be handled now...I think

[krisgesling]

Looks fantastic!

Thanks!