* Improve explanations of network, hybrid, and lattice parsers
* Remove dead code from parser comparison notebook
* Clean-up notebook variables to reduce size and make diffs cleaner
* Revert changes that were peripheral to the core changes
* Clean up the parser comparison notebook
* Address issue where hybrid didn't honor the columns parameter
* Fix dropping of empty rows/columns in hybrid
* Hybrid learns table y-dimensions from lattice
Create hybrid parser leverage both lattice and network techniques.
Simplify plotting of pdf in lattice case.
Rename "parser.table_bbox" into "parser.table_bbox_parses", since it
represents not a bbox but a dict of bbox to corresponding parsing data.
Still missing: more unit tests, plotting of steps.
No longer rely on the mode but on the parsing analysis during network
detection.
Added unit test for complex table with vertical header and mixed
horizontal / vertical text.
Frh