GitLab

* Remove obsolete parts from the /etc/default/snf-image sample file
  shown in the configuration section.
* Update the documentation about having made the img_passwd an
  optional parameter.

Replace all references of `environmental variable' with `environment
variable'

 * Fix various spelling errors
 * Add module comments on all python utilities

In the image directives always use relative paths for images that are
hosted inside the project's repository.

Update the documtation to reflect the changes made to support
NetBSD and OpenBSD systems.

Split the section `Image IDs and Storage backends' to decouple
the actual feature, the logic and the configuration. Feature and
logic is moved to a new section under 'Architecture' and the rest
remain under 'Usage'. Also add examples for each case.

Also fix various typos

Add a section under Architecture about the Image Configuration Tasks

Fill in the architecture section of the documentation