Cleaned up return logic

- ReturnNodes are explicitly added during compilation
 - ReturnNode is used instead of scattering "return" throughout
   code compilation snippets
 - nodes gain a make_return method in order to do the most useful
   thing when a return is requested

lib/optparse.js

@@ -63,6 +63,7 @@
             _d.push(' ');
           }
           return _d;
+          return null;
         }).call(this).join('') : '';
         let_part = rule.short_flag ? rule.short_flag + ', ' : '    ';
         lines.push("  " + let_part + (rule.long_flag) + spaces + (rule.description));
@@ -70,6 +71,7 @@
       return "\n" + (lines.join('\n')) + "\n";
     };
     return OptionParser;
+    return null;
   }).call(this);
   // Helpers
   // -------
@@ -93,6 +95,7 @@
       }).call(this));
     }
     return _a;
+    return null;
   };
   // Build a rule from a `-o` short flag, a `--output [DIR]` long flag, and the
   // description of what the option does.