Replace the Error() object with an error() function which takes fmt

formatspecs, making for much cleaner code. Reformatted everything.

This actually happened in multiple steps but then I corrupted my local
repository and I had to recover from the working tree.

lib/fluxsource/fluxsource.h

@@ -79,7 +79,7 @@ class EmptyFluxSourceIterator : public FluxSourceIterator
 
     std::unique_ptr<const Fluxmap> next() override
     {
-        Error() << "no flux to read";
+        error("no flux to read");
     }
 };