Add support for fubu style cli tools to create *.cli.xml files for FubuDocs

[mtscout6]

In fubu style command line apps like ripple, st, and others there is a built in command dump-usages which generates an xml file that can be consumed by FubuDocs. We need some rake tasks that will do this as part of the build so the docs stay current with changes to the cli tool.

[jeremydmiller]

+1