To update the `fftpack` package about fftpack

[zoziha]

I am happy that fpm supports native flag settings (see my discourse help).
I have just 2 months of ample time recently, and I am very happy to set up an interface for fftpack to make a long-term development attempt.

My current done job (added fpm support for two version of fftpack):

I simply migrated netlib/dfftpack1.0 (fftpack4.0) to the branch fortran-fans/fftpack4.0 (License: public domain), and initially added fpm support;
At the same time, I simply migrated john/fftpack5.1(F90) to the branch fortran-fans/fftpack5.1 (License: GPL), and initially added fpm support. Obviously, it currently depends on -fallow-argument-mismatch.

My request (make two PRs):

I want to submit the above two versions of the fftpack package to your repo at the same time. My suggestion is to create a separate branch for fftpack4.0 and merge fftpack5.1 into your master branch (or a new branch named fftpack5.1). What do you think?
If you agree, you need to create a fftpack4.0 branch for me in your this repo, then I will make two PRs, thank you~

Potential problem (LICENSE):

Now I have not specified any license for these two packages, I am not familiar with it myself, and all licenses are kept as they are.

Modified @2021-07-16

Maybe I think I should avoid the GPL license.