Crate origin_trial_token

Expand description

Implements a simple processor for https://github.com/chromium/chromium/blob/d7da0240cae77824d1eda25745c4022757499131/third_party/blink/public/common/origin_trials/origin_trials_token_structure.md

This crate intentionally leaves the cryptography to the caller. See the tools/ directory for example usages.