Allow Zone file to be created from a template

[WetHippie]

Follow up from #101 to allow for putting in the file as content. If the $content parameter is non-empty use it as first preference.

[inkblot]

I've been hesitant to add direct control over zone file content to this module. Conventional zone file handling defeats the option to configure a dynamic zone, which is a necessary precondition for using some of the advanced features of the module. This seems appropriately limited in scope, though. Just a couple of minor clean ups and it will be ready to merge.

[inkblot]

Also, do you mind too much if I squash the branch in the merge?

[WetHippie]

Yes, sure. It will be a couple of days until I get to your other comments.