Bridgehead Nitrogen Heterocycles. Part-V. Syntheses of s-Triazolo[3,4-b][1,3,4,]benzothiadiazines, s-Triazolo[3,4-b][ 1 ,3,4]thiadiazines, s-Triazolo[3,4-b][1,3,4]thiadiazino[5,6-b]quinoxaline, lmidazo[2,1 -b]benzothiazole and Benzimidazo[2,1-b ]benzothiazole as Potential Antimicrobial A gents