GBK support

[yesvods]

Some websites are in GBK encoding. Default covert method can't handle this well.

[msindwan]

Hi @yesvods, to determine if it's an issue with the encoding of the mhtml doc or some of the assets, could you provide an example of a GBK-encoded website that isn't handled well by mhtml2html?

[yesvods]

Hi @msindwan
Such as the website below.

http://www.ce.cn/xwzx/gnsz/gdxw/202003/22/t20200322_34538471.shtml

[gaomeng1900]

If anyone still need this. I fixed it in my fork. mht2html