Add Lock Types

[danii]

Add lock types. I've already described these in #1 before we split this into it's own pull request.

[timothee-haudebourg]

Sorry you've been waiting a long time for this. So to be clear, you want to add a family of traits for thread-safe data structure. I like the idea, but I don't like the Lock name which I find confusing. Maybe we can just reuse the same name as the non-thread-safe ones, but put everything in a sync/concurrent/thread_safe module.

[timothee-haudebourg]

Also I really need to add a CI for this crate.