Should diffdf care about data frame class

[kieranjmartin]

Right now diffdf doesn't care if one object it compares is a tibble and one is a data.table, as they are both data.frames. I'm thinking it probably should? At least generate a message about it

[gowerc]

So I think we should flag this but that by default it should just be done as a note.

We could add (yet another) option to raise this as a warning instead ?

[gowerc]

thinking about this some more I don't think we should check for this. Thinking from a QC perspective all we care about is that the contents have been derived correctly. Wether the user chose to use data.table or tibble or data.frame shouldn't really matter at all I don't think.

The current implementation in #67 prints the object type out in the summary but doesn't raise an error if they are different. I think I am happy with this implementation, let me know if you feel different @kieranjmartin