TS-2576: Add Oct/Hex escape representation into LogFormat

Introudce two escape representations into LogFormat:
* Oct escape sequence:
  '\abc': a,b,c should be one of [0-9], and
          (a*8^2 + b*8 + c) should be greater than 0 and less than 255.

* Hex escape sequence:
  '\xab': a,b should be one of [0-9, a-f, A-F], and
          (a*16 + b) should be greater than 0 and less than 255.

Signed-off-by: Yunkai Zhang <qiushu.zyk@taobao.com>