Initial experiment with diffing using shift-resistant blocks
Fix whitespace in test data!
Fix diff function to cope with changes right at the start of the streams
Make Diff object-oriented
Make Diff objects easy to read
Rename Chunk._data to Chunk.source
Handle ording of overall diff correctly and stop...

inefficiently finding previous common chunks repeatedly by using a "Block"
class.
Simplify return type of diffing, build whole diff structure in order
Add insertion into data_a for testing...

Yes, yes, real testing, and so on.
Make Diff handle insertions in A data
Add len (of virtual combined stream) to Diff
Improve/clarify diffing algorithm
Blocks.__repr__ for debugging
Fix virtual indexing if DiffHunks to account for interim unchanged data...

and simplify.