Change tagging scheme for documentation branch

[GoogleCodeExporter]

we currently tag the documentation branch sequentially:

documentation-1
documentation-10
documentation-11
documentation-12
documentation-13
documentation-2
documentation-3
documentation-4
documentation-5
documentation-6
documentation-7
documentation-8
documentation-9

While this works well,
1) it's not clear which software version corresponds to a documentation tag and 
2) it doesn't order nicely when listing tags. 
So I'd like to propose to change the scheme to

documentation-[version]-[increment]

e.g. documentation-0.8.6-a.

Original issue reported on code.google.com by westm...@gmail.com on 15 Jul 2014 at 3:19