Make clearer parquet docs and error messages

[lokijuhy]

Fixes

• Documentation: Added Supported File Formats page to documentation. Preview the docs here.

  • Fixes #12

• Gives a more detailed error message when a user tries to interact with parquet files when they don't have a parquet engine installed. Previously, the user got an ImportError (thrown by pandas). Now, that same error message is prepended with additional text, so the error in full reads:

  ImportError: Parquet engine must be installed separately. See ImportError from pandas:
  Unable to find a usable engine; tried using: 'pyarrow', 'fastparquet'.
  pyarrow or fastparquet is required for parquet support

  • Author Comment: I don't want to say anything specific in the datatc error message about pyarrow or fastparquet specifically, because the ImportError comes from pandas, not datatc itself - This whole error comes from the fact that pandas has a to_parquet method yet does not include a parquet engine in its install requirements. So, I don't want to write an error message that just make things more confusing if pandas's dependencies/requirements change in the future. All together, I'm not sure my addition to pandas's error message adds anything valuable, and in fact I think it sounds "un-pythonic". But I gave it a try. Please let me know your opinion on whether the additional description is worth it, or how to make it sound better.

Misc

• Documentation: added general intro to front page of docs. Preview here.

[lokijuhy]

.... maybe it's worth mentioning as Aron was having a similar error and didn't know what to do when dealing with parquet files...

This is definitely worth documenting somewhere. I think Notion might be more appropriate. I don't want to put specific instructions in datatc itself that will likely go out of date with future changes to pyarrow/macOS.