Imidazo[1,2-b]pyridazines. X. Syntheses and Central Nervous System Activities of Some 3-(Acetamido, benzamido, substituted benzamido or dimethylamino)methyl-2-(phenyl or substituted phenyl)-6-(halogeno, alkylthio, alkoxy, phenylthio, phenoxy, benzylthio or benzyloxy)imidazo[1,2-b]pyridazines