Time stamp error for Windows

[leochan2009]

time stamp don't get updated, even the computer is made to sleep for a while.
See the commit:
leochan2009@e042cb4

And the CI build resultes:
https://ci.appveyor.com/project/openigtlink/openigtlink-wg8dx/build/1.0.145

[tokjun]

The use of multiple TimeStamp class instances might have caused this issue.

clock() (high-res clock API for Windows) only gives time from CRT initialization, while gettimeofday() in Linux/Mac gives the time since the Unix epich (1/1/1970 00:00:00 UT). To make them compatible, the current implementation of TimeStamp reset the internal origin time stamp with a time stamp from time() with a resolution of second in the constructor, measure the time from the internal origin time stamp to the GetTime() call, and combine them. However, this does not work well when one tries to compare time stamps from two different class instances with a sub-second resolution, because the origin time stamps in the two instances are measured with a second resolution.