Fix CurrentRuby docs: it's path-active ruby, not invoking ruby.
Tweak CurrentRuby docs.
v0.17.4 - refactoring, rdocs (thanks to Thomas Stratmann) and an experimental git feature.

- SystemProfile and its associated classes underwent a major refactor (that I started at Railscamp 13). They're a lot more readable now, much more thoroughly tested, and more predictably extendable. I'm still not 100% happy with them because they use a lot of inheritance, but they're in good shape now.

- String::Colorizer was refactored into Babushka::ANSI, and its internals reworked and simplified. It generates minimal escape sequences now, in less code (and with more tests). I also added String#colouriser for us Aussies and Brits, and deprecated some unneeded methods.

(The only remaining parts of babushka that aren't properly covered with specs are quite old. As I refactor them I add the missing tests.)

- Thanks to Thomas Stratmann for a pull request adding rdocs to CurrentRuby.

- Finally, I've added the --git-fs commandline option, which causes babushka to commit the result of meeting deps to a git repo at the root directory. This feature is experimental and might change in the future; it's part of a new technique I'm working on to manage servers.