[BUG] prospector should warn about unknown options

[rnestler]

Describe the bug
If I have a typo in my configuration options (or try to use an unexisting option), I'd expect that prospector raises a warning or an error.

To find out how to configure mypy I had to look at the source at https://github.com/PyCQA/prospector/blob/master/prospector/tools/mypy/__init__.py until I found out that I need to do

mypy:
  options:
    warn:
      - unreachable

Instead of

mypy:
  options:
    warn-unreachable: true

To Reproduce
Steps to reproduce the behavior:

1. Add an unexisting option to .prospector.yaml
2. Run prospector
3. prospector just ignores it

Expected behavior
Prospector should warn or raise an error

Environment (please complete the following information):

• OS: Linux
• Tool mypy
• Prospector version 1.5.1
• Python version 3.8.10

Additional context
It would have helped me enormously if there was a verbose or debug mode, where I could see how exactly mypy gets called.

[adamcunnington-gdt]

(and the docs need to be more exhaustive)

[AtomScott]

I'm having a lot of trouble configuring mypy. I think warning about unknown options would be a good idea. The docs need to be more exhaustive too.

How would one go implement such warnings?

[carlio]

I'm not familiar with mypy nor did I write the prospector mypy integration so I'm not 100% sure what each of the options do. However, I have added an exception which is raised if an option is not recognised, along with a unit test to validate it: c163370

@AtomScott or others, if you would like to improve the documentation and add more robust testing for other value parsing issues in the mypy tool, please go ahead and raise a PR. The commit above should help point you at the right place to start, but if you have questions please ask!

[sbrunner]

Are you sure that the list is exhaustive?
In the documentation I see many options starting with e.g. warn-* that's not in the list...
https://mypy.readthedocs.io/en/stable/command_line.html#configuring-warnings