[CHANGE] Service#params excluded from API

The method has been made private.
It wasn't expected to be readable from outside of the service.

== Changes

* Service#params
[CHANGE] Service parameters excluded from the API

All the methods: .params, #params, .allow_params and attributes it adds became private.
Neither the .allow_params helper, nor parameters aren't intended to be used outside
of the service object.

Basically the service object should contact to outer world via .new, #run and #subscribe only.
In some cases the object can allow dependency injection or accessing its callbacks via

== Changes

* .allow_params became private
* .allow_params declares private getter(s) and setter(s) for allowed parameters
* .params became private
* #params became private