feat: upgrade deps, new prefix option, cleaning and typos

[GreyXor]

Hello, this PR contains a few improvements:

• An update of all dependencies
• A few typographical corrections
• use of any rather than interface{} or http.NoBody, rather than nil
• A new prefix option

This new prefix option is useful when you have an API whose server spec contains a subfolder. In my case, it's /api. But as I register my api with server.RegisterHandlersWithBaseURL(s.EchoServer, server.NewStrictHandler(s.APIService.API, nil), "/api").
The prefix is not visible to the router, so the validator can't see it either. Setting this new option to /api virtually removes the prefix. And makes the validator work properly.

close: #11