Documentation: expose missing docstrings for csp objects

[melissawm]

For example, csp.ticked is mentioned but could benefit from having its docstring exposed. This is probably true for other objects as well.

We can use this issue to capture a list of objects that need to be documented better.

[pavithraes]

Noting a couple more:

• CSVReader & CSVWriter adapters
• csp.Outputs & csp.output
• Several functions in https://github.com/Point72/csp/wiki/CSP-Node#anatomy-of-a-cspnode can be noted in the API Reference as well
• ParquetOutputConfig

[timkpaine]

RE CSVReader/Writer, i think we should rewrite from scratch xref #259