Determine how package attributes/files might be templated using package metadata

[nacl]

It was pointed out in the review for #173 that we may want to expand various template attributes (e.g. the version) to other parts of the RPM spec file, such as the %description.

This raises another larger point: what attributes of packages should be template-able? In many cases, it might make sense to subject all of them to template substitution, for example, some filesystem paths are annotated with versions, like those in /usr/share/doc in CentOS.

Another important part of this is figuring out the templates' syntax and how they're to be processed in a cross-platform manner.

[aiuto]

Yes. The more the merrier. The idea in #198 allows us to bring a dict of string->string mappings into any of the rules so that we can expand it in any way we need. Any rpm spec template is a possibility

[aiuto]

This is getting old and not specifically actionable. Closing to clean out the backlog.