fix: Use werkzeug directly instead of uc-rfc6266-parser, to apply security updates

[jpmckinney]

uc-rfc6266-parser depends on werkzeug, but I'm quite sure uc-rfc6266-parser is not maintained (just like rfc6266-parser was not maintained, and rfc6266 before that).

I kept the same logic as:

https://github.com/genme/python-rfc6266-parser/blob/3a7f39db61eb1dbda9be6568150e75b7a805f050/rfc6266_parser.py#L209-L214

and https://github.com/genme/python-rfc6266-parser/blob/3a7f39db61eb1dbda9be6568150e75b7a805f050/rfc6266_parser.py#L148

and https://github.com/genme/python-rfc6266-parser/blob/3a7f39db61eb1dbda9be6568150e75b7a805f050/rfc6266_parser.py#L61-L85

[Bjwebb]

Released in https://pypi.org/project/libcoveweb/0.26.0/

[jpmckinney]

Thank you!