Make threadsafe

[chrisbloom7]

1. The base Enumpath module sets up a number of module level variables (@verbose, @logger, and @path_cache) that make this library not threadsafe. This was initially done to avoid needing to instantiate an object, i.e. Enumpath.apply('food.0', party), and so that state didn't need to be passed around to all of the operators and processors. Our approach to this should be considered alongside Investigate re-implementing a version that caches segment types #3.
2. Memoization using ||= (which may not be threadsafe) in Enumpath::Path#cache
3. For things that may be shared across threads, like the logger or path cache, ensure no instance variables are used
4. MiniCache is not threadsafe :( Maybe we need to expose a way to BYO cache store? (This is on my future feature list anyway) Or roll something similar with concurrent-ruby, et al?)
5. to_regexp appears to be threadsafe, but we should verify