Add "Spine", formally representing partial ML files.
WIP: simplify History, (split zipper/lexer and real history part)
WIP: remove Lexer definitions from History
WIP: Cleanup Zipper interface (in Misc)
Spine: cleanup
WIP: Replacing wip implementation
WIP dégueulasse
Switching Outline, Chunk and Typer to Spine.
WIP: Everything switched to Spine
Slowly fixing things…
Fix synchronisation code
Spine: more general interface
Add support for typing modules
Typer: catch warnings
Command: History.seek_(forward/backward) semantics slightly changed
Spine: assertion on wrong position
Outline: location was computed incorrectly
Fixing errors
Fix Spine integration, all tests pass!