Generalize adapters

[pirfalt]

chi.Mux, gin.Engine, gorillamux.Router, http.HandlerFunc and negroni.Negroni all implements the http.Handler interface, and all there adapter files are strikingly similar. All the adapters could probably be replaced with a single adapter which takes that http.Handler interface instead of the concrete implementations.

Which I noticed after opening #17 which adds this to only the handlerfunc package a new httpadapter package. (Which all others could delegate to).

[sapessi]

PR merged. Closing issue. Thanks for the contribution @pirfalt and apologies for the delay!

[kyleyost19]

To this point being made @pirfalt , you can just remove the gorillamux and handlerfunc packages. You simply cast them to an http.Handler when you instantiate your Handler package with Handler.New().