Wrap and Display Width Should be Specifyable independently

[brodieG]

For example, would be useful to allow a super wide display width to capture wide data frames without display wrapping, but then wrap the resulting diff so that it fits in a narrow terminal. This eliminates the complexities caused by the display wrap of 2D structures on the diff. Incidentally, the HTML mode pretty much works this way already since the wrapping is handled by the browser/viewier.

[brodieG]

Be sure to update the docs for ?diffPrint, particularly the "Matrices and Data Frames" section once this is done.