Get binary_trees benchmark working.

Wren is actually doing well in it:

wren      mean: 1.9441 median: 1.9428 std_dev: 0.0260
lua       mean: 3.5992 median: 3.6033 std_dev: 0.0156
python    mean: 3.6667 median: 3.7097 std_dev: 0.1340
ruby      mean: 1.3941 median: 1.3914 std_dev: 0.0091

src/wren_compiler.c

@@ -401,12 +401,13 @@ static void readString(Parser* parser)
         case '"':  addStringChar(parser, '"'); break;
         case '\\': addStringChar(parser, '\\'); break;
         case 'n':  addStringChar(parser, '\n'); break;
+        case 't':  addStringChar(parser, '\t'); break;
         default:
           // TODO(bob): Emit error token.
           break;
       }
 
-      // TODO(bob): Other escapes (/t, /r, etc.), Unicode escape sequences.
+      // TODO(bob): Other escapes (\r, etc.), Unicode escape sequences.
     }
     else
     {