Interrupt Collector and Parser

Changes: (The major ones are really for `/proc/interrupts`)

1. Collector updated:
  * Collector for `cpuusage` and `cpuhz` updated to collect per core rather than aggregated.
  * Collector for `top` updated to have `-c` flag so can see command used to generate process.
  * Collector for `/proc/interrupts` added so can get interrupts per core and IRQs.
  * Collector for `netstat -s` added to collect `netstat` statistics.
2. Parser Metric for `/proc/interrupts`.
3. Added log example for `/proc/interrupts` with a configuration file example.
4. Updated example logs for `sar.cpuusage.out` and `sar.cpuhz.out` to be per core now.

Can you define a new method ```is_header_line(self, line)``` instead of manually checking for ```if 'CPU' in line```? We did that sort of thing in ```sar``` and other older metrics, but its really not a good idea.

That method can be used in ```find_header()``` as well.