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.

... 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.

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