Support for bleach 6

[marksweb]

Bleach 6 has been released and is due to be the final version of bleach because it is now deprecated due to html5lib being unmaintained. Further details here.

The significant changes required to support version 6 are;

• bleach.clean, bleach.sanitizer.Cleaner,
  bleach.html5lib_shim.BleachHTMLParser: the tags and protocols
  arguments were changed from lists to sets.

    bleach.clean(
        "some text",
        tags={"a", "p", "img"},
        #    ^               ^ set
        protocols={"http", "https"},
        #         ^               ^ set
    )

• bleach.linkify, bleach.linkifier.Linker: the skip_tags and
  recognized_tags arguments were changed from lists to sets.

     bleach.linkify(
         "some text",
         skip_tags={"pre"},
         #         ^     ^ set
     )