Add example for accumulate2

Author: erichaney

examples/accumulate2

@@ -0,0 +1,8 @@
+(reduce2 + [1 2 3 4]) # -> 10
+(accumulate2 + [1 2 3 4]) # -> @[1 3 6 10]
+
+(reduce2 + []) # -> nil
+(accumulate2 + []) # -> @[]
+
+(reduce2 max [1 4 2 3 9 5]) # -> 9
+(accumulate2 max [1 4 2 3 9 5]) # -> @[1 4 4 4 9 9]