[docs] Add examples to documentation

[jstockwin]

Closes #48, and as a side effect closes #56.

I've temporarily published the version of the docs from this branch, to help with the review. You can view this here: https://py-pdf-parser.readthedocs.io/en/doc-examples/

• Check docs build correctly in CI
• Make docs nicer to edit locally (livereload etc)
• Add changelog to docs
• Add examples:
  • Simple example
  • More complicated example
  • Table extraction
  • Complicated table extraction (page breaks, non-simple)
  • Example with sections
  • Example which shows visualise tool in detail
• Add tests to ensure examples always work (and hopefully helps to keep them up to date)
• Update the overview page

[pauloAmaral]

Very nice examples! I have a few comments but nothing big.

Also, do you think it would be too much to add a few screenshots of the PDFs in the first and second examples? I think it would help to understand what you're reading if you see the elements you are trying to extract data from (1st example) and creating the sections (2nd example) without having to go back and forth from docs and PDF. But no big deal, up to you!

[pauloAmaral]

Awesome 🥳 🥳 🥳