started working on this with the idea of fixing #1623, although I
realized that this was actually just a documentation issue around
a toml eccentricity.
closes#1623
* Adding Varnish HTTP Cache input plugin
* Applying PR feedback
- Linked to varnish in input README
- Updated README/CHANGELOG
- Cleaned up sampleConfig to remove formatting
- Shorted lines to 80 chars (except where test input requires long strings)
- Using internal.RunTimeout to wrap call to varnishtat
- Added dummy file for windows