Simplify incremental parsing interface

Functional proof of concept, more code can be dropped
Remove dead code from merlin_parser
Simplify type checker
Work only on 4.02.1
Update TODO
Rename Makefile.ocamlmakefile -> Makefile.merlin
Travis: use only 4.02
PoC PPX
PPX: add support for caching cookies
Emacs: rework error display infrastructure
New indexer runs inside merlin and doesn't require a db
PoC of interface reverse dependencies \o/

["users","of","module","Std"]
Indexer: index implementation