Remind count of map and add benchmark #142
                
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the old:
BenchmarkCount
BenchmarkCount-8 2150287 514.2 ns/op
the new:
BenchmarkCount
BenchmarkCount-8 393898780 2.755 ns/op
And otherwise ,the insert from
the new
BenchmarkItems-8 278 4242234 ns/op
the old
BenchmarkItems-8 258 4090206 ns/op
Fixes: #143