Move file argument to print function

[gowerc]

This has always stood out to me as a bit odd here. I propose we move it to the print function which is more akin to how other packages handle it (for example xtable)

[kieranjmartin]

So I think my one reluctance on this is that I think diffdf could in theory be used by quite novice R users (i.e. ex SAS users who want to do proc compare), who won't know about the print method (i.e. they just know that when they run the code they get something on their console, and want to save that as a text file). I have some thought on the saved output btw but will make a seperate issue

[gowerc]

Hey @kieranjmartin ,

I can appreciate the appeal of making it more accessible to SAS users, but I don't think this should come at the expense of intuitiveness to R users as most other packages that implement a file= options typically do so in the print method. I think the best thing for SAS users would be better documentation and examples perhaps an FAQ ?