Figure out how to document both web-sys and stdweb

[jstarry]

Description

Need to figure out how to handle https://docs.rs documentation. Ideally we would be able to host docs for both stdweb and web-sys. There aren't a lot of web-sys/stdweb types in the Yew API really so this might not be too big of an issue.

Proposed Solution

• Ship a new crate for yew called yew-stdweb which is documented for stdweb types
• Default to web-sys in docs.rs/yew docs
• Link to https://docs.rs/yew-stdweb from https://docs.rs/yew