Fixed #22943 -- Correctly serialize compiled regexes.

Thanks to antialiasis at gmail dot com for the patch.
Fixed #20631 -- Increased the default EmailField max_length to 254.

Thanks pmartin for the report.
Corrected domain max length for EmailValidator; refs #20631.

Thanks MarkusH for the report.
Ensured bound field renders as unicode safe data

Refs #22950.
Fixed #22950 -- Eased markup customization for choice field rendering

Thanks Patrick Robertson for the report.
Fixed #22960: Bad handling of relations as PKs in autodetector
Merge pull request #2881 from charettes/ticket-22943-compiled-regex-deconstruction

Fixed #22943 -- Correctly serialize compiled regexes.
Fixed an alphabetization in AUTHORS

"Eric Palakovich Carr" should be sorted by "P", not "C".
Added a space before explanation of "Invalid HTTP_HOST header: ..."
Updated tests per previous commit.
Fixed flake8 indentation.
Fixed various minor doc typos / references.
Fixed #21832 -- Updated prompt, tests, and docs to show that USERNAME_FIELD supports FK. Refactored code to allow overriding for custom behaviour.

Thanks Chris and Tim Graham for review.