string - 字符串操作函数

本页文档由[这个文件](https://gitee.com/openLuat/LuatOS/tree/master/luat/../lua/src/lstrlib_exts.c)自动生成。如有错误，请提交issue或帮忙修改后pr，谢谢！

本库有专属demo，[点此链接查看string的demo例子](https://gitee.com/openLuat/LuatOS/tree/master/demo/string)

string.toHex("\1\2\3") --> "010203" 6
string.toHex("123abc") --> "313233616263" 12
string.toHex("123abc", " ") --> "31 32 33 61 62 63 " 12

string.fromHex("010203")       -->  "\1\2\3"
string.fromHex("313233616263") -->  "123abc"

local tmp = string.split("123,233333,122")
log.info("tmp", json.encode(tmp))
local tmp = ("123,456,789"):split(',') --> {'123','456','789'}
log.info("tmp", json.encode(tmp))

-- 保留空片段, 2023.4.11之后的固件可用
local str = "/tmp//def/1234/"
local tmp = str:split("/", true) 
log.info("str.split", #tmp, json.encode(tmp))

string.toValue("123456") --> "\1\2\3\4\5\6"  6
string.toValue("123abc") --> "\1\2\3\a\b\c"  6

local str = "abc"
log.info("str", str:startsWith("a"))
log.info("str", str:startsWith("b"))

local str = "abc"
log.info("str", str:endsWith("c"))
log.info("str", str:endsWith("b"))

local str = "\r\nabc\r\n"
log.info("str", string.trim(str)) -- 打印 "abc"
log.info("str", str:trim())       -- 打印 "abc"
log.info("str", #string.trim(str, false, true)) -- 仅裁剪后缀,所以长度是5