merlin-imenu: restructure code & handle exceptions (#639)
merlin-imenu: restructure code & handle exceptions (#639)

* merlin-imenu: restructure code & handle exceptions

* minor update

dra27/merlin,rgrinberg/merlin,rgrinberg/merlin,ocaml/merlin,rgrinberg/merlin,rgrinberg/merlin,the-lambda-church/merlin,the-lambda-church/merlin,dra27/merlin,the-lambda-church/merlin,ocaml/merlin,ocaml/merlin,dra27/merlin,dra27/merlin,ocaml/merlin