Update for clang compiler.
Simplify CPUTime and RunTime classes.

Remove empty base TimeMeasurementBase. Remove virtual qualifiers.
Correct doxygen documentation.
Specify internal or external linkage explicitly.
Use same precision as the rest of the algorithm.
Remove extra ';' after member function definition.
Use std::size_t instead of size_t or replace int's with std::size_t.
Use DISALLOW_COPY_AND_ASSIGN macro.
Remove unused private attribute.
Remove if which cannot be true.
State missing enum values explicitly.
Remove unreachable code.
Use std::abs instead of global fabs.
Using return value of GeoLib::mergePoints().
Removed unused value COLUMN from enum GEOTYPE.
Added (virtual) destructors to GMSH mesh density classes to avoid warnings.
Initialized attribute _glyphSource in init list to avoid warning.
Initialized attribute _item in init list to avoid warning.
Initialized attribute _lineFilter in init list to avoid warning.
Fix spelling of doxygen instruction.