* add unlabel.ml which parses interfaces and removes labels in function declarations and docstrings. This is a quick hack, but it does the job.
* an attribute [@keep_label] can be added to the labelled arguments to mark labels like ~cmp which should stay in the "unlabelled" interface
* While augmenting the labelled interfaces I stumbled across some inconsistencies between the currend labelled / non-labelled interfaces. I used the labelling that made most sense to me and added a "FIXME" comment.
* Maybe we should break backwards compatibility at some point and name the comparison arguments to the sorting functions in CCArrayLabels.ml ~cmp instead of ~f ?
