add auth template that is a bit more general

Directives:

* auth_type
* auth_name
* auth_digest_algorithm
* auth_digest_domain
* auth_digest_nonce_lifetime
* auth_digest_provider
* auth_digest_qop
* auth_digest_shmem_size
* auth_basic_authoritative
* auth_basic_fake
* auth_basic_provider
* auth_user_file
* auth_require

This patch is still incomplete. E.g. directives for authentication providers and
authorization are missing.
remove obsolete documenation for auth_basic_file
use puppet syntax highlighting in README.md
add documentation for auth* directives
remove template nesting (does not work)
Merge pull request #289 from booo/auth

Auth