Btype, Env: Expose management of internal state
Rename Chunk_parser to Raw_parser
Introduce new, simpler grammar (for merlin2 w/ custom menhir version)
Errort_report: remove lexer errors
Raw_parser: make stack structure slightly more explicit
Switch to new Clflags interface

sed -e 's/!\(Clflags.[a-z_]\+\)/\1 ()/g' \
    -e 's/not \(Clflags.[a-z_]\+ ()\)/not (\1)/g' -i.bak *{,/*}.ml
Warnings: explicitly manage state
Env, Btype: adjust cache interface