Allow options.type to be a function (constructor) when building.
Expose AbstractAscoltatore so such a function can inherit from it and pass
ascoltatori module exports so there is no requirement on e.g. a mosca app
to import ascoltatori.
Test to check we can get an AbstractAscoltatore instance by specfying the
constructor when building.
Emit ready in the test after setting up methods.
Merge pull request #52 from davedoesdev/backend_type_as_function

Allow options.type to be a function (constructor) when building.