* adding fortran tutorial
* [fortran/en] fixing some typos
* [fortran/en] changed a word
* [fortran/en] changed another word
* [fortran/en] typos and improvements.
* [fortran/en] moving comments around
* [fortran/en] moving print statement introduction to appropriate section
* [fortran/en] changing exit code to generic error code
* [fortran/en] changing bessel_j0 (available from fortran 2008) to log10 (available since fortran 77).
* [fortran/en] being explicit about using cleaner Fortran 2003 notation
* [fortran/en] code whitespace consistency
* [fortran/en] adding examples on implied-DO loops.
* [fortran/en] small adjustment to implied-DO loop example to make it more idiomatic
