integrated hex mesher based on r-tree in gui and parser

Common/Context.h

Common/DefaultOptions.h

Common/Options.cpp

Common/Options.h

Fltk/optionWindow.cpp

Geo/GModel.cpp

Geo/GRegion.cpp

Geo/GRegion.h

Geo/Geo.h

Geo/gmshRegion.cpp

Mesh/Generator.cpp

Mesh/meshGRegion.cpp

Mesh/meshMetric.cpp

Parser/Gmsh.tab.cpp

Parser/Gmsh.tab.hpp

Parser/Gmsh.y

Parser/Gmsh.yy.cpp

benchmarks/3d/Cube-01.geo

benchmarks/centerlines/bypass_centerlines.geo

benchmarks/stl/BifurcationRemeshCurvature.geo