Re-indent code

(using `ocp-indent -i jitsu.ml`)
Style improvements

* remove unecessary Lwt wrappings
* remove parenthesis
Normalize indentation of main.ml

(ocp-indent -i main.ml)
More style changes
More tweaks

* Enable all warning (but the one which are annoying)
* Make the whole project compile again
Add jitsu.mli
Remove trainling whitespaces
Remove an other Lwt wrapper
Merge pull request #1 from samoht/master

Style fixes