rtklib rpm package

Sorry that I use english here.

I know many of us use Linux. And I want improve user experience by creating rtklib rpm build.

It would be greate if you can test this build and feedback.

Spec-file at github

Build for Fedora 32 and RHEL/CentOS 8

Also srpm

If all good I will add it to the official Fedora and RHEL/CentOS 8 repo.

I am not add any changes to the source code except correcting building environment.