Document input keywords in docstrings

[haneug]

Is your feature request related to a problem? Please describe.
Currently, all simple keywords have a comment describing their use (more or less detailed) but these comments are not included in the API documentation.

Describe the solution you'd like
For the auto documentation to work with these comments they must be converted to docstrings. Optimally, they should also be refined. Docstrings describing the keywords in the blocks would also be good to have but may be limited to the most used block keywords.

• Initial docstrings for simple keywords.

Blocks with working docstrings:

• Block CPCM
• ...