UPDATED LIBRARY:
- added DERIVATE module. containes routines to evaluate jacobians, gradients and
derivative of functions, D and C, subroutine and function form.
- moved grids generation into a separate module ARRAYS.
- moved error and convergence evaluation into ERROR module.
- rename SLPLOT/SLREAD to IOPLOT/IOREAD and associated headers file, so to have a
better naming convention. Updated to F21.12 (was F18.10).
- VECTOR algebra module is now entirely independent.
- fix bug in STATISTICS when evaluating histograms
- avoid using linspace in FFTGF. NOTE that FFTGF needs a serious update.
Possibly avoiding default use of MKL library. It would be better to
rely of FFTW3 or FFTPACK. Some tests are in order.
- TOOLS added function to evaluate order of magnitude of a real
Merge branch 'devel'

Conflicts:
	src/TOOLS.f90