benchmarks: add InNaive, fix Hz units display

sysfs: Improve coverage for thermal

- Correct minor typos.
- Improve sysfs-thermal error wrapping.
- No significant functional change.

Remove the warning in README.md about versioning.

Now that v1.0.0 is being released and will use a proper versioning mechanism,
there's no need for this warning.

Clients will be able to use http://github.com/golang/dep to version this
library.