Publish all docs to docs.rs

[ethanfrey]

Along with #196, this will make it much easier to understand and use the libraries.

cosmwasm_std and cosmwasm_storage are the prime targets as they will be used the most by contract developers and should be well documented (and self-documenting).

Look at https://docs.rs/serde/1.0.112/serde/ for an example

[webmaster128]

Publishing to docs.rs is done automatically via cargo publish. See the right column of the table in the main README.

[ethanfrey]

I'm blind... cool they are there. However, they definitely need to be improved.

https://docs.rs/cosmwasm-storage/0.8.1/cosmwasm_storage/ is a bit confusing

But https://docs.rs/cosmwasm-std/0.8.1/cosmwasm_std/ is no help to get oriented (unless you know which types to look for)