Add `fortran-lang/stdlib` package (branch: stdlib-fpm)

[zoziha]

Originally, I wanted to submit fftpack (has been passed, #53 ) and stdlib-fpm together, but found that it seems that fpm-registry does not support branch analysis like this:

[stdlib]
"latest" = { git = "https://github.com/fortran-lang/stdlib", branch = "stdlib-fpm" }

Is this an issue?

[awvwgk]

Try pretending it is a tag and try again, in git there is no practical difference between the two.

[zoziha]

I tried to submit #55 , and an error occurred in CI (see CI failed). @awvwgk Maybe I misunderstood what you mean.
Do you mean so:

[stdlib]
"latest" = { git = "https://github.com/fortran-lang/stdlib", tag = "stdlib-fpm" }

or,

[stdlib]
"latest" = { git = "https://github.com/fortran-lang/stdlib", branch = "stdlib-fpm" }