Set CurrentVoltage to a pointer so it can be null

fixes #80
Merge pull request #88 from StackExchange/windows

Fix Windows Process Metrics
Merge branch 'master' of github.com:StackExchange/scollector
Fix some comments
Move descriptions to constants
Disable metadata during print mode

fixes #67
Sort
Sort, fix, and uniq-ize the names
Use AddTS to copy CPU timestamp from WMI