Fortran filesystem

add lib_path() function that tells path to libfilesystem.[dll,dylib,so] if compiled as shared library

rearchitect code to deduplicate Fortran interfaces

fallback code is mostly in C now, for use from other C programs and for didactic purposes

remove Meson build system due to Meson bugs and since more probably use FPM now.

bugfix getenv to not crash if variable not found

more checks. Generally most function that return a path return empty string if something goes wrong