Add support for Jinja 3.1

[jyelloz]

Jinja 3.1.x has removed the jinja2.Markup function which was deprecated in Jinja 3.0.x which now causes the template functions in this package to break.

Added some fallback imports just to reduce the possibility of breakage with users running the latest version of typogrify and older versions of Flask/Jinja for whatever reason.

See:

• https://jinja.palletsprojects.com/en/3.1.x/changes/#version-3-1-0
• https://github.com/pallets/jinja/pull/1544

[justinmayer]

Many thanks for the enhancement, Jordan! 🥇