Versioning

[plbt5]

Hi Ian,
I've done some work on versioning of documents, and made a branch to represent that stuff. It's a kind of hack to use git for document storage, and overlay that with a versioning scheme aligned with git's versioning.
Check it out, and if you like it, please merge it. It is a simple preprocessor and can be ignored if it's irrelevant. The only prerequisite for its use is that the folder that one uses for one's document, is under git control.

Its implementation uses:

• the YAML configuration. I used my pandocomatic-elsarticle.yaml for that.
• the elsarticle.latex template, since that merges the version number into the document during preprocessing.
• the test_eslarticle.md as small test file to ... well... test :-)

Best
Paul