build: pin version of `atdgen`
typo in sleep
Merge pull request #14 from hammerlab/sleep-typo

Typo in sleep
Fix typo: "developping" --> "developing"
Fix type: 'persistance' should be 'persistence'
Fix typo: 'persistance' should be 'persistence'
Merge branch 'master' of https://github.com/hammerlab/ketrew
Fix typo: 'Persistance' should be 'Persistence'
Merge branch `master` into `dev`
Merge branch `master` into `dev` again

Conflicts solved:
	src/lib/ketrew_command_line.ml
	src/lib/ketrew_target.ml
lib: fix and improve the Target graph clean-up

It used to be based only on dependencies; now it takes everything into
account. The clean-up algorithm is not “complete” but conservative: a
target that is not activable could resist the garbage colletion because
a target in its transitive sub-graph is still activated or running
(which should not be indefinite).
lib: improve “versioned” serialization

This commit

- adds versioning for happenings and measurements, and
- forces better versioning everywhere through a better functor in
`Pervasives.Json`: `Make_versioned_serialization`.
lib: expose function `Target.to_json`
lib: get rid of the last `Json_raw` (in `Server`)