Initial sqldiff commit.

The two csv files a short examples for experimenting.
They are sourced from the same dataset, but randomized so they only have partial
overlap and so they are *out of order*
I've arranged, also, that they share two blocks of identical rows near the starts.
Import my SQLdiff paper scrap notes
Checkpoint: first functional table diffing algorithm.

Slow, verbose, and the API isn't full there, and it only detects
changes as adds or deletes, not updates, but it runs.
Useful sqlite script
Describe the algorithm I used; import thoughts on plugging into the larger system.
stub out tests
Added some basic tests, which found critical bugs; wrote a simpler impl to shake them out.
Wrote applydiff() and made the simpler diff() impl pass its tests.