modified unstables to use enumerators
caching get_abslocs in MakeSet in dug.ml
use usual add and find for Table
optimize unstables : returns (key, old value, new value) list
optimize compare : not to use polymorphic function
added tail recursive list reverse function
optimize join_pairs and widen_pairs
hashing in Table
Merge branch 'master' of github.com:skcho/zooberry