ReadFrom, WriteTo and Max

[it512]

add ReadFrom and WriteTo function
add Max UUID

[bormanp]

Please provide a justification for adding these two functions. I understand that these implement io.ReaderFrom and io.WriterTo signatures but there needs to be a good reason for these functions such that they "carry their own water" as they say.

[it512]

1 UUID作为一种类型，在一些编码和解码场景需要直接的io.Reader和io.Writer和操作，从而减少零时对象的生成，和方便使用
2 在网络编程中，可以直接从net.Conn中读取/写入UUID
～～～～～～～～～～～
1 UUID as a type requires direct io.Reader and io.Writer operations in some encoding and decoding scenarios, thereby reducing the generation of temporary objects and making it easier to use
2 In network programming, you can read/write UUID directly from net.Conn