[linux] fill SwapMemoryStat.Sin/Sout from /proc/vmstat
 * fix IOCountersStat
Merge pull request #23 from def/master

[linux] fill SwapMemoryStat.Sin/Sout from /proc/vmstat
fix error getting CPUInfo on darwin.
readLinesOffsetN helper for reading only specific part of the file
CPUTimes percpu for Linux
CPUTimes percpu for FreeBSD
CPUTimes percpu for Darwin
CPUPercent