fanfiction.net re-enabled

This version re-enables fanfiction.net support.

Installation instructions:

Install attached plugin zip file, or use Calibre's 'Get plugins' feature.

FanFicFare is delivered as a pip Python package.

pip install FanFicFare
or
pip install --upgrade FanFicFare
...to update.

(pip will automatically install dependencies.)

Run fanficfare -h from command-line.

Add better chapter error reporting, refactor proceed_question code.
Add plugin options to mark success/failed/chapter error individually.
Clear metadata cache after adapter metadata fetch. Cached metadata values may not be replace_metadata processed if fetched before their conditional dependencies. Revealed by AO3 one-shots using title for chapter name.
Re-enable ffnet and bump up sleep times for same.
ffnet fpcom, continue_on_chapter_error:true by default, increase sleep times.
First rough version of reporting continue_on_chapter_error chapters.
Report chapter_error in custom error column and marked (when configured).
Update to cloudscraper v1.2.52
Increase times between retries on fetch error.
Tweek ffnet/fpcom sleep times again.
slow_down_sleep_time: randomize between 0.5 time and 1.5 time.
Report cloudscraper exceptions as such, plus hide the potentially misleading 'opensource' part.
adapter_fanficsme: do an extra fetch before login for cookie(?) Closes #633
adapter_webnovelcom: Fixes for site changes. Closes #629
quotev.com: site change in date parse, use utf8:ignore as first encoding choice. Closes #625