Small cleanups
Add JRuby 9.2.11.0
ruby-builder.js - Win32 - use C:\Windows\system32\tar.exe
Document mingw and mswin in the README
Add JRuby 9.2.10.0
Add TruffleRuby 20.0.0
Add support for jruby-head
Add support for .tool-versions
Add notes about Windows in the README
Cleanup PATH for JRuby on Windows * That way we remove the default Ruby in PATH which was confusing.