Restrict CI to supported build versions.
Removed 1.8 from build system.
Moved C-API headers.
Removed 1.8 from the VM.
Removed 1.8 from kernel.
Merged 2.1 kernel files into regular files.
Removed 1.8 from Gemfile.
Fixed removing C-API include dir.
Added ignores for generated C-API.
Fixed C-API header require.
Removed 1.8 from the C-API.
Removed Rubinius.ruby18|21?.
Fixed compilation issues.
Removed 1.8 from instructions.def.
Removed version-specific files from load_order files.
Removed debugger.
Fixed loading kernel.
Removed unused Rubinius::Loader.main.
Fixed 2.1 merge of IO.
Fixed 2.1 merge of sprinter.