Make ` command behave like irb with coloring

- And `` command to run selected lines, but removing ``` as
  that can be done by making a new buffer and writing in that.

include/internal/scripting/ruby.h

@@ -120,5 +120,5 @@ struct Block {
 };
 
 void register_basic(BEd &ctx);
-void run(BEd &ctx, const std::string &str);
+std::string run(BEd &ctx, const std::string &str);
 }; // namespace bed::internal::scripting