Aaron Patterson

Hi, I've noticed Semian has a few globals that aren't thread safe, or at least they're shared among threads. For example [this consumers instance variable, the LRU cache](https://github.com/Shopify/semian/blob/d10e5366174ecb4dc47ffe40092379a1a3957cfc/lib/semian.rb#L259-L266), and [this...