We should make `<versionFile>` mandatory and specify options for its behaviour

[martindholmes]

As suggested by @joeytakeda on #115:

I think empty <versionFile/> should just be "I don't want a version extension" and <versionFile>VERSION</versionFile> (where VERSION doesn't actually exist) would be "I don't care what it is, so just make it for me"; otherwise, there's no way that someone could decide not to have VERSION'd files. In terms of what we'd generate as the version, we could just do [a-z0-9] (to avoid any potential conflicts). And since we're using Saxon 10, we can use random-number-generator() to generate a unique six character version code (I hadn't had a chance to use it yet, but just played around with it and it's great. Would send a xsltfiddle, but neither xsltfiddle nor xquery fiddle has support for Saxon 10 at the moment apparently).

This would go along with making the element mandatory in the schema.

[martindholmes]

The fix for issue #305 merged today into dev is an interim fix pending what we decide to do on this ticket.

[joeytakeda]

Decisions:

• <versionFile> should be mandatory
• If <versionFile> is empty, random string is generated
• If <versionFile> is not empty, but can't find the file, then random string is generated
• If <versionFile> is not empty and it can find the file and it has content:
  • Replace spaces with nothing
  • Take the first 64 characters of this — but recommend shorter versions in the documentation
• Remove the automatic Git VERSION creation from the test build
• Make the documentation point to EDITION file for its own build