Add basic scripting support.

- Fix certain bugs in ruby parser
- And a lot more cleanup/minor fixes.

include/bed.h

@@ -6,6 +6,7 @@
 #include "internal/functions/suffixes.h"
 #include "internal/io/io.h"
 #include "internal/marks/marks.h"
+#include "internal/scripting/ruby.h"
 #include "internal/theme/theme.h"
 #include "internal/ui/command.h"
 #include "internal/ui/text_mode.h"
@@ -21,6 +22,8 @@ struct BEd {
   std::unordered_map<std::string, internal::syntax::Language *> languages;
   internal::io::IO io;
   internal::vase::AppendStorage append{"/tmp"};
+  mrb_state *mrb = nullptr;
+  int arena;
 
   bool help_mode = false;
   bool prompt_mode = true;