feat(fortran): Added fortran bindings

Building of the C API GridFire can now be used from fotran using the
gridfire_mod fortran module. This exposes the same, limited, set of
funcitonality that the C API does.

tests/extern/fortran/meson.build

@@ -0,0 +1,5 @@
+executable('test_fortran_extern', 'gridfire_evolve.f90',
+  install: false,
+  fortran_args: ['-Wall', '-Wextra'],
+  dependencies: [gridfire_fortran_dep]
+)