Support Google Wallet API

[kogai]

Hey, thanks for the great library!

I have an API that would like to add supported APIs of google-apis-rs, so please listen.

It is Google Wallet API, which offers to operate loyalty cards or airplane tickets or else in the Google Wallet app.
Since this API has Discovery Document here, but Google Discovery Service hasn't shown it in the list of APIs, as and consequence, the API has also not been included in google-apis-rs.

Could you please consider adding this API to the crates under this repository?

FYI, I got to be able to generate a client by trying to put the Discovery Document URL and other information into apis.json in the repository I forked.
https://github.com/kogai/google-apis-rs/compare/0998b2810e91ab7b76847c859f339ed14e57d014..b9bd9f385af94048547628d9f7d678e4a57759d4

[Byron]

Indeed, the top-level discovery document is a copy of an older request made against the google discovery endpoint, and won't contain the latest APIs for that reason.

The fork posted here seems like it could be a PR that can be merged, and I am encouraging you to bring the Google Wallet API to the parent repository that way.

Thanks a lot!

[kogai]

Sounds great!
I'll PR right away 👍