Improvement on NcmSplineCubicNotaknot and NcmABC.

Improved spline_cubic_notaknot algorithm (faster and simpler).
Improved tests on spline_cubic_notaknot.
Fix several minor memory leaks, racing conditions. Functional version of NcmABC and NcABCClusterNCount.

Improved log functions on NcmFit, NcmMSet and NcmDataset.
Fixed old leak in cvode functions.
Fixed bug in NcmStatsVec for online covariance estimates for weigthed samples.
Fixed several minor bugs and leaks.
Added mutex lock to avoid threads problems in _nc_matter_var_prepare_fft.
Included cubature for systems without libcuba.
New NcABCClusterNCount for ABC analysis of cluster number counts.