Request: Support for precompiled Ruby binaries

[jwarner112]

Note: I've written this with the goal of tasking myself with implementing it myself, and just want to gather early opinions and feedback before committing the time.

I've been looking at Fullstaq Ruby and noticed #76 where it asks about ASDF supporting their project. Because this Ruby plugin is coupled so heavily to ruby-build, the creator of Fullstaq doesn't anticipate being able to do this integration without modifying the plugin, first.

All that needs to happen is for the plugin to be able to recognize when a precompiled binary needs fetched. It could be through pattern-matching the string, or through something more sophisticated, perhaps inspired by the Golang plugin. Thoughts?

[Stratus3D]

I think this is already being discussed on #57, lets continue the discussion there.