Make plugin list in PDF docs readable

[andrewdotn]

The current PDF docs attempt to format the list of all plugins as a
table, without any word-wrapping of the plugin description. That results
in almost all the information getting cut off. This PR formats the same
information into more of a paragraph format for the PDF, with nothing
cut off.

• Allow maintainers to push and squash when merging my commits. Please uncheck this if you prefer to squash the commits yourself.

[andrewdotn]

Sample output, starting on page 126:
pytest-better-plugin-list.pdf

[bluetech]

Thank you, this looks good to me.

It would have been nice if there were some "responsive" table format, i.e. one that could self-adjust to the page dimensions, but I guess there isn't?

[andrewdotn]

With sphinx, there is a way to set automatic width with wrapping for a column, but when the table has more than 30 rows, sphinx flips over to using the LaTeX longtable package to get the a table that supports having page breaks inside it. And that package doesn’t support automatic-width columns.

With longtable, one can specify that a column has a specific width and gets wrapped, e.g., p{2in} for a 2-inch-wide column, but I don’t think that’s a good long-term option because it would take a lot of manual tuning to look ok, and anyone publishing a new pytest plugin or updated package description to PyPI could dramatically change the required widths.

Another alternative I considered, before going with this PR, is to flip the pages with the table to landscape mode, possibly with a larger page size for just those pages.

[bluetech]

OK, that sounds good!

[wimglenn]

@andrewdotn I wonder if you have any ideas to make this table render better? This is what it looks like to me in Chrome browser / macOS - "last release" column way too narrow, and there's a lot of wrapping with hyphenation characters for some reason rendering as a box. Maybe the "status" and/or "requires" column(s) could be dropped, they don't have much useful info and it would allow the others to be wider.