add: wasm target

[tetuaoro]

Hi Monsieur Chone,

I don't know if these changes work because I'm poor xD. I'm starting a new project and I want to use this crate on the client side (hydrate and csr).

Changes

I used target instead of feature config to target wasm or non-wasm because some crates already implement wasm in their crate.

Thanks for this great library and happy to contribute to your project. Let me know what you think about my impl.

EDIT: related to #11

[jeremychone]

@tetuaoro

First, thanks for the contribution.

To be honest, I am a little worried about how intrusive the WASM support will be to the code. I understand the appeal, but not being an expert in Rust/WASM, I am going to be cautious on this one.

Do these changes work for you in WASM?