**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.
