**NOTE: Please try to break this and tell me where it is insufficent.**

Allows only whitelisted tags and attributes through.

The setting ALLOWED_TAGS can override the behavior. The syntax of
this setting is a space-separated list of tags, which are optionally
followed by a colon and a comma-separated list of attribute permitted in
the tag.

For example, to allow <a> tags which are links or named anchors, but not
to allow definition of an onclick attribute:

    ALLOWED_TAGS = "a:href,name"

In your templates, sanitizing is easy.

    {% load sanitizer %}

    {{ user_comment|allowtags|safe }}

    {{ user_comment|allowtags:"b i"|safe }}

Disallowed tags or attributes are simply removed.

In some cases, it is useful to disallow a tag, but to convert it to something
safe, rather than stripping it entirely. For example, you might not want to
allow <h1> tags, and want to "quiet" them into <h2> tags.

    {{ body|maptags:"h1=h2 h2=h3 h4=h5" }}

