full clean-up of the auth-docs; feel free to shake out any

nits, if there are (probably there *are* :)

main changes:

- introduce docs for mod_authn_default, mod_authz_default and
  mod_authz_user
- fix argument lists of the provider directives
- fix the examples (intended to be better :)
- introduce the AuthDigestShmemSize directive
- remove AuthDigestUser/GroupFile
- mention htdigest in AuthUserFile docs
- mod_authn_anon is now an authn provider
- markup

Reviewed by: Astrid Ke�ler <kess@kess-net.de>


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@97823 13f79535-47bb-0310-9956-ffa450edef68