Rework incremental typer for 4.02
Working recovery!
Command: reimplement dump env
WIP integration of menhir DEFAULT
Std: enhance Zipper interface
Myocamlbuild: ignore menhir tag warnings
MERLIN_LOG: Dump responses as comments

This allows to directly pipe MERLIN_LOG output to another merlin instance
BrowseT: simplify interface, document
Merlin_typer: add dump function
Code cleanup/reindentation
Command: add [dump,typer,input] to print raw input sent to typer
Parser: tweak recovery heuristics