(#1554) Add support for all common compressions (write and read)

- Remove the context.Context interface and export the *context, the iris.Context now points to the pointer\nSupport compression and rate limiting in the FileServer\nBit of code organisation


Former-commit-id: ad1c61bf968059510c6be9e7f2cceec7da70ba17

_examples/convert-handlers/negroni-like/main.go

@@ -39,6 +39,3 @@ func negronilikeTestMiddleware(w http.ResponseWriter, r *http.Request, next http
 	w.WriteHeader(iris.StatusBadRequest)
 	w.Write([]byte("Bad request"))
 }
-
-// Look "routing/custom-context" if you want to convert a custom handler with a custom Context
-// to a context.Handler.