Move all the constraints in there own module

src/lib/all.mlw

src/lib/constraints/add.mlw

src/lib/constraints/boolPresent.mlw

src/lib/constraints/constraints.json

src/lib/constraints/dune

src/lib/constraints/dune.generated

src/lib/constraints/dune.template.generated

src/lib/constraints/equiv.mlw

src/lib/constraints/generator/generate_simple.ml

src/lib/constraints/isTrue.mlw

src/lib/constraints/le.mlw

src/lib/constraints/not_.mlw

src/lib/constraints/or.mlw

src/lib/constraints/simple.template.mlw

src/lib/cp.mlw

src/lib/dune