a2f27bd62d
This commit allows clients to derive an InteHEAD::TimePoint (renamed from InteHEAD::Date) from a calendrical start point (std::time_t) and an elapsed time in seconds. This is generally useful for restart purposes which needs to fill in Y-m-d H:M:S information in INTEHEAD and has other uses as well. Demonstrate utility in a new unit test that also shows leap year handling. While here, also add fractional second resolution to the time-point handling. INTEHEAD(411) already has microsecond precision and we should leverage that support.
opm-common
Contains common components used throughout all of OPM, in particular CMake modules for the build system.