2-Oxoglycosyl ("Ulosyl") and 2-Oximinoglycosyl Bromides: Versatile Donors for the Expedient Assembly of Oligosaccharides with beta-D-Mannose, beta-L-Rhamnose, N-Acetyl-beta-D-mannosamine, and N-Acetyl-beta-D-mannosaminuronic Acid Units