benchstat: rename Benchstat→Metrics, BenchKey→Key

These will work better in the eventual package benchstat API.

Change-Id: I95c63f2fe7c1a0f6db09afbe9776539f264a577c
Reviewed-on: https://go-review.googlesource.com/35933
Reviewed-by: Quentin Smith <quentin@golang.org>
1 file changed