- update/review all fftw related operators + doc

- Update doc

fix install process
review tests process
fix (partial) arnoldi stuff which depends on lapack
...

Fix penalisation/subsets (partially)
Update doc (sphinx)
Almost all tests ok except:
	 22 - mpi_test_advec_scales (Failed)
	 77 - test_advection_nullVelocity (Failed)
	 79 - test_advection_randomVelocity (Failed)

Update differential_operations and stretching (fix bug + optimizations) - Add GlobalTests (test functionnalities, perf ...)