Fortran interfaces

[GiovanniBussi]

@ralf-meyer I tried to add fortran interfaces to your patch. This is something that we provide as of PLUMED 2.8, and that enables type checking of the arguments passed to the cmd() functions.

There is a modification in the patch script here. It basically:

• copies an additional file to Modules and adds it to the related Makefile
• adds use plumed_module statements in several source files

I also created a branch on this repository to test it.

What do you think?

Thanks!

[ralf-meyer]

This is great! I am strongly in favor of any changes that improve readability and aid future maintenance! It is also a great starting point for me to add support for cmake compilation to the patch.

[GiovanniBussi]

@ralf-meyer thanks I merged the modification to master.

Regarding cmake, you might want to take inspiration from dftbplus.