improved definitions per #358

[gregfowlerphd]

Fixes #358

[gregfowlerphd]

@johnbeve: Done

[cameronmore]

@gregfowlerphd The repo restructuring might have been the cause of the conflicts on the other branches, but these still look like they are able to merge easily.

[gregfowlerphd]

@cameronmore: Thanks, Cameron. :)

[neilotte]

Good eye @gregfowlerphd

[gregfowlerphd]

@neilotte: Thanks, Neil. :) I admit I'm still not entirely sold on using the "instance of" locution in these definitions but not in class definitions, but since that seemed to be the consensus choice (such as it were), I thought it best not to rock the boat.