Revise benchmarks:

- Ditch JS since it's in a different league.
- Make binary_trees and fib run faster.
- Compare using best time instead of mean.

benchmark/fib.wren

@@ -9,7 +9,7 @@ var fib = fn(n) {
 var start = OS.clock
 var i = 0
 while (i < 5) {
-  io.write(fib.call(30))
+  io.write(fib.call(28))
   i = i + 1
 }
 io.write("elapsed: " + (OS.clock - start).toString)