• use the festest golang aes ctr implement with golang 1.9

• go1.9.2 aes ctr (BenchmarkAESCTR1K_goAesCtr)

1000000	      2336 ns/op	 436.15 MB/s

• CL 51670 (BenchmarkAESCTR1K_thisAesCtr)

3000000	       467 ns/op	2178.83 MB/s

Unless otherwise noted, the Go source files are distributed under the BSD-style license found in the LICENSE file.

• folk code from golang CL 51670 (https://go-review.googlesource.com/c/go/+/51670) (golang/go#20967)
• change package name to AesCtr
• copy internal package from golang1.9.2
• add ctr test to this package. (aes_ctr_test.go)