Reduce number of calls to ref_pg_vol in DGVolume.
Add -Ofast and parallelize DGMacroCellInterface
All omp parallelization now over macroelements.
Clean up and localize some variables.
Parallelize RK2 loop and change mesh to disque.
Fix bug in .msh path.
Parallelize DGVolume on the subcells (faster than on macrocells).
Make DGVolume memory acces coalescent.
Update small and vsmall values.  Use disque as default msh.
Put OpenMP pragmas behind #ifdef _OPENMP for when openmp is not available.
Use cmake to detect and set openmp flags if available.
Add disk meshe and geometry from master branch.
Merge branch 'master' of github.com:phelluy/SCHNAPS into openmp

Conflicts:
	CMakeLists.txt
	src/field.c
	src/interpolation.c
	src/schnaps.c
Use OpenMP instead of pthreads.
Improve multi-threading.