Add an optional chruby-install function (install.sh) which calls ruby-build then updates RUBIES.
If/when setup.sh is spun off into ruby-install, we can switch off of ruby-build.
Is the thinking here that ruby-build is superfluous given it isn't very difficult to install Ruby?
Yeah, plus I don't like how ruby-build requires to be updated when a new version of Ruby is released. Our future ruby-install script should be able to accept arbitrary versions, and construct the URLs / paths.
Code-spiked and refactored scripts/setup.sh into ruby-install. Warning: it's a weekend code-spike, probably doesn't work, still a work in progress. Also still needs proper option parsing.