整理代码，新增string扩展模块，把一些小模块合并进string和table扩展模块中

parts/modes/drought_n.lua

@@ -21,7 +21,7 @@ return{
 		mStr(R>=0 and R or 0,69,265)
 	end,
 	score=function(P)return{min(P.stat.row,100),P.stat.time}end,
-	scoreDisp=function(D)return D[1].." Lines   "..TIMESTR(D[2])end,
+	scoreDisp=function(D)return D[1].." Lines   "..STRING.time(D[2])end,
 	comp=function(a,b)return a[1]>b[1]or a[1]==b[1]and a[2]<b[2]end,
 	getRank=function(P)
 		local L=P.stat.row