ENH: pdfly extract-tables using the camelot lib

[Lucas-C]

We could provide a new extract-tables subcommand, thats uses the camelot to extract tables from PDF files.

The PR implementing this should include:

• unit tests
• documentation: docstrings & a new page in docs/user/
• the command output should display the .parsing_report from camelot
• it should be possible to target specific PDF pages
• various export options should be possible, using the corresponding camelot methods: to_csv() , to_json(), to_excel(), to_html(), to_markdown() & to_sqlite().
• other options could be implemented immediately or in further PRs: --password for decryption, --flavor, --parallel, --split-text

[Lucas-C]

I juste realized that camelot already has a CLI script: https://camelot-py.readthedocs.io/en/master/user/cli.html

I opened this issue to discuss this with the camelot development team: camelot-dev/camelot#639

I'm removing the good first issue, hacktoberfest & up-for-grabs labels from this issue, in order to allow some time for discussion before starting to implement this: maybe we should just mention camelot CLI in pdfly documentation & output, instead of introducing a new extract-tables subcommand?