Update proxyserver.go

build gonc_386 compatible with Win7

fix typo

update docs

mkdocs

upgrade dependencies

Optimize SOCKS5 UDP

Optimize UDP Session

update link usage

Add link/linkagent for bidirectional proxy and enhance httpserver paths

- Introduce link and linkagent modes (similar to socks5local/socks5server)
- Allow link to listen on proxy ports on both local and remote sides
- Proxy ports support both HTTP and SOCKS5 protocols
- Support SSH-like -L / -D / -R forwarding modes via link
- Allow httpserver to accept multiple paths (files or directories)