specfile: add libvalidator0 subpackage
specfile: split libvalidator0 further into -devel package

As per the Fedora Packaging Guidelines, a -devel package must be used
for unversioned shared object files (the libvalidator.so file):

  https://fedoraproject.org/wiki/Packaging:Guidelines#Devel_Packages

This fixes the "devel-file-in-non-devel-package" rpmlint warning.
Merge pull request #17 from mgeisler/subpackages

Create RPM subpackages