swap out beautifulsoup for a string.replace to avoid html reformatting

[kbehlers]

see #28 . BeautifulSoup closes tags in unexpected ways during parsing, particularly because of its use of the python built-in 'html.parser'. I encounter similar mangling when using the middleware with certain custom tags.

This removes the dependency on BeautifulSoup to prevent any mangling. It is formatted with Black

django-debug-toolbar does something similar to this merge request, albeit with re.split and str.join instead of the simpler str.replace.

[kbehlers]

@tjwalch Any chance of this PR getting accepted?