Convert HFTI and H12 Fortran subroutines into C++

[BenJuan26]

Having Fortran subroutines necessitates either providing precompiled object files or making Fortran compilation part of the build process. Neither is particularly ideal, so the best thing would be to eliminate the Fortran altogether.

[BenJuan26]

The conversion is mostly done, and for now is in the file focas_fortran.cpp in the dev branch. However, I've had some difficulty accounting for the way h12 utilizes Fortran's strange memory management for arrays (dimensions).

For reference, the algorithms are described in the book Solving Least Squares Problems (1974).