Add default method for more generics giving warning about no implementation for this class

[athowes]

And yes seems reasonable to add default method for non-implemented classes giving a warning. Will add issue.

Originally posted by @athowes in #70 (comment)

Suggest to add default method for (all) generics giving a warning that nothing is implemented for that generic. Perhaps could say what classes it is implemented for and how they could get their object to that class (i.e. they need to use epidist_prepare or something like that).