Fortran 2003 (initial implementation)

Hi!  I saw this benchmark with a bunch of different implementations, and thought that I'd give it a go.  It currently is not very efficient, running about the speed that the Oracle Java implementation does (when compiled with gfortran) on my computer, but I thought I'd create a PR and see if you/others were interested.

(Mostly I just wanted an excuse to play around with some of the new 95-2003 language features (structural types, modules, recursive functions, etc.)