Remove unused :strict attr from host file store

It seems like the attr on the object was never used in the way it was meant to
be.

Maybe `HostFileStore#delete` was supposed to look like this instead:

      def delete(host)
        sync do |buffer|
    -     delete_host host, buffer, :strict
    +     delete_host host, buffer, self.strict
        end
      end

... but I don't recall enough how it was indended to be used to make that
change right now.
Freeze default section name
Require specifying a token delimiter when used as lib

As per #49