basic Fortran mode

This is a basic Codemirror mode implementation for the Fortran language. Should be work for f77/2008. 
I'm still a javascript newbie so probably many improves could be done, but I guess it's a good start. 

I've taken keywords and builtins from the Pygment's [FortranLexer class](https://bitbucket.org/birkenfeld/pygments-main/src/7304e4759ae65343d89a51359ca538912519cc31/pygments/lexers/compiled.py?at=default#cl-1435) and used the pascal mode as base.