htmlmin: starting to port to bs4

I will find a better way to not minify script, pre and textare. Then I
will start fixing other issues (in the first moment#21, #33 and #37).

Related to #25.
authors: update file

Including emails.
htmlmin: change the placeholder for tags that should not be minified

Related to #20.
tests/resources: fix tags

bs4 sorts tag attributes.

Related to #25.
htmlmin/tests: don't use assert_equals
htmlmin: fix pep8 issues