File logger

Merge pull request #2 from SwiftRex/FileLogger

Add file logger

Fix issue and improve ergonomics

LoggerMiddleware needed conformance with... well... Middleware protocol!
Convenience init now became a .default() factory, which allows the middleware to be generic only over a single generic parameter, the inner middleware (or IdentityMiddleware) that already contains all parameters for describing actions and state.

Latest SwiftRex

Update SPM reference to latest SwiftRex

First official release

First official release!