Improve code annotations and integrate with docs

[mariajgrimaldi]

We should have a way of automatically generating documentation for each filter, just as it happens with openedx-events: openedx/openedx-events#316
Also, in-line docs for each class should be improved. Another thing we should do is to make available the different versions on the docs page

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1. docs: add configuration for automatic filters docs generation #173
   open-source-contribution +1
2. Improve in-line documentation for each filter class

[mariajgrimaldi]

I removed the link so this issue doesn't when merging the first task.