RUBIES -> chruby_detect_all_rubies

[skull-squadron]

Fix/supercede #278, #291, #314, #316, #318, #320, #345, #350, #363, #364

It's necessary to eliminate RUBIES environment variable to add/remove missing rubies in real-time and to save time. Keeping it around would be just pointless, technical debt tyranny.

[postmodern]

BTW, I eventually switched to your style of logic of re-searching the rubies directories each time.
c87f4cf

[skull-squadron]

No big deal. I've been migrating things to use XDG conventions and work cleanly in contexts of non-root user, system, and vendored activation, similar to Python's virtualenv.

There is greater work to be done in shells and scripting:

• package management like zplug
• running faster by JITing
• loading commands as native shared objects
• simplification (zsh reminds me of Haskell and nix)
• avoiding unnecessary forking

[postmodern]

@steakknife I'm super curious about XDG conventions and the shell. While XDG has been embraced by Linux GUI apps, it hasn't really been embraced by shell utils (that I've seen) and macOS users/developers still haven't adopted XDG.