Add fpm package manifest

[awvwgk]

• support usage of functional-fortran with fpm
• does not support testing due to shortcomings of bootstrap fpm

Fixes #17

[milancurcic]

Thanks a lot @awvwgk. Did you check that fpm build works?

[awvwgk]

Of course, checked with bootstrap fpm and GCC 10.2.

[milancurcic]

Great, thank you.

One more thing: I think the package name should be just "functional". Rationale: The repo name "functional-fortran", like with "datetime-fortran" was a branding decision. It allowed it to stand out, and, putting words "functional" and "Fortran" together helped it get attention. However, in the context of fpm and Fortran packages, the word "fortran" is redundant.

I did the same with datetime-fortran, which as an fpm package is just datetime.

What do you think?

[milancurcic]

Thank you!

[certik]

Yes, the name should be just datetime and functional.