Added grid sequencer with horizontal sequencing logic
Refactored sequencer logic out for simplified testing
Refactored tabling logic out for simplified testing
Added test case for vertical sequencer.

Added vertical sequencer by transposing table and reusing horizontal sequencer.
Added vertical sequencer to sequence returned by grid sequencer
Fix transposer to return lists of lists instead of lists of tuples
Bugfix table transpose operation.

Stub out left diagonal sequencer (LDS).

Implemented test cases for LDS
Fix iteration of grid on boundary
More boundary & negative test cases
Rough implementation of algo
Add in vertical travel to rough impl
Wrapped it all up with test case for the grid sequencer
Factored out a product helper function from various locations.

Emit answer for problem 11.
Merge branch 'problem11'