Build NGINX from source with nginx.ng state with support for passing
compile time flags necessary for installing modules such as more headers
by the openresty project.

* removed override releasever variable use for CentOS

the debian package installs the nginx service just fine, but the extra
fifo->syslog functionality would be nice to have under debian as well.

Fixes #39.

Fixes GH saltstack-formulas/nginx-formula#14.

* Fixing iteration for building nginx by source with respect
  to modules
* Adding `CHANGELOG.rst` and `VERSION` per https://groups.google.com/forum/#!topic/salt-users/zHguqsk-mds