randstr包用于生成指定长度的随机字符串，综合参考了java apache的org.apache.commons.lang3.RandomStringUtils类和nodejs random-string模块，三者的核心算法都是通过产生随机索引从指定字符集中逐位获取字符。
用法示例：
/** * @date 2020-09-04 * @author pengpengzhou <philip_chow@163.com> */ package main import ( "github.com/pochard/commons/randstr" ) func main() { //letters + numbers println(randstr.RandomAlphanumeric(17)) //letters println(randstr.RandomAlphabetic(17)) //numbers println(randstr.RandomNumeric(17)) //letters + numbers + other visible ascii chars println(randstr.RandomAscii(17)) //specified chars println(randstr.Random(17, "abcde123")) }输出：
Ix13J89u0Cffnz6A1 VortohsdgsybJaOeX 55587050455303745 *$=%Ms2yEhe]zs-jk bd132322cd22b333a
