benchmarks: add bent

Add David Chase's bent package to perf. Cloned from:
  https://github.com/dr2chase/bent

Change-Id: I43d2d65cbd5ee171a5d123d78d6d748625a49836
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/290431
Trust: Jeremy Faller <jeremy@golang.org>
Run-TryBot: Jeremy Faller <jeremy@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
32 files changed