ref: update for go mod

[coolaj86]

• add go mod tidy to add go.mod and go.sum
• move benchmark into its own subdirectory (to prevent test/benchmark dependencies leaking through)
• move examples into their own subdirectories (fixes linter errors)
• go fmt ./...

[coolaj86]

In addition to this PR, the repo would need to be tagged:

git tag v1.0.0
git push --tags