Fix ProcTime.StartTime on Windows

[andrewkroh]

This converts the process creation time from Windows epoch to milliseconds since unix epoch. A test was added to sanity check the StartTime value.

Process creation and exit times are points in time expressed as the amount of time that has elapsed since midnight on January 1, 1601 at Greenwich, England.

Source: https://msdn.microsoft.com/en-us/library/windows/desktop/ms683223

[codecov-io]

Current coverage is 70.58% (diff: 100%)

Merging #52 into master will decrease coverage by 0.02%

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  Partials         61         61          

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[tsg]

LGTM, waiting for travis.