Daff

- Removed a RNG dependency in the tests.
- Updated link to description of data protocol

- Update `daff.js` to https://github.com/paulfitz/daff/commit/2106718 (2017-06-23)
- Improve `print` and `summary` functions
- Handle duplicate column names (fixes 16)
- HTML table generated by `render_diff` now uses DataTable javascript library to provide

- fixed header row
- pagination (10,25,50,100,All)
- filtering
- column visibility (individually enable/disable)
- copy/csv/excel/pdf export buttons
- column reorder (drag and drop)
- row reorder (drag and drop)

- Lots of improvements thanks to gwarnes-mdsol
- `render_diff` now defaults to `pretty=TRUE`.
- Use inline CSS instead of obsolete `<center>` tag.
- Improve Output Formatting and Add Support for Daff Flags
- Update daff.js to version 1.3.25.

- added summary for patch, thanks to jsta, feature request 12

- updated daff.js library to 1.3.16, thanks to jeroenooms, solves issue 9

- changed internal I() into JS() thanks to jeroenooms