New version of filename revving recipe

This version is more suitable for importing, whereas the previous
version was based more around the idea that you'd copy and paste it
into your project's build.xml file.

The task and properties have all been renamed for clarity. The example
invocation target has been moved alongside the documentation.
An index file for importing all recipes en masse.

The premise here is that you'd import the index from your project's
build.xml, and it would in turn import each of the individual
recipes. So far only rev.xml is accounted for.