RFC7009 Missing revoke/tokens revocation feature

[JonathanHuot]

Oauthlib supports tokens revocations but requests-oauthlib does not provide a way to use it.

See https://oauthlib.readthedocs.io/en/latest/_modules/oauthlib/oauth2/rfc6749/clients/base.html#Client.prepare_token_revocation_request

[Louson]

Hello, is there any reason to not have this feature or can we suggest a PR ?