Remove IOCountersForNames that was recently added in favor of variadic function with same capabilities.
Operates like disk.IOCounters, but accepts an array of names to limit the results.
This code is based on the FreeBSD version and implements roughly the same feature set.
This enables using gopsutil in a codebase that gets built on other OSes than the ones supported. Instead of a build failure as before, due to the build tags, gopsutil will now throw an "not implemented" runtime error. Fixes #234.
Daniel Nelson