BREAKING CHANGE: all previous `nginx` based configurations must be reviewed;
`nginx.ng` usage must be promoted to `nginx` and any uses of the original
`nginx` will have to be converted.

With this one can now also write

 - include:
   - file1
   - file2

Rather than only

 - include: file1
 - include: file2

on openSUSE Leap 15.0, the string was systemd.cpython-36

like openSUSE and SLES

to reduce duplication of constants

... by providing a pillar string. I developed this for use in
combination with ext_pillar and file_tree to deploy letsencrypt
certificates.

default value if dhparam isn't defined in the pillar.

Improvement - Disable reload of nginx when enabled=False (previously the nginx was always reloaded if settings.config != None; even with enabled=False)

In order to improve security and ease of use, added creation/generation
of dhparam file.

Removed comment after testing that this change works with xenial

Fixes #70