* TODOs

** Breaking

*** TODO Why does ~add_pid~ take a ~filter~
*** TODO Don't expose all of the constants from ~kqueue-sys~
*** TODO Express which filters are appropriate for which functions in the type system
*** TODO Watcher is a trait, ~UncheckedWatcher~ and ~UncheckedWatcher~ impl it
*** TODO Redo API kinda like notify's
*** TODO use ~OwnedFd~ instead of ~RawFd~
*** TODO Use our own error type
*** TODO ~get_event~ should return a custom error if not started, rather than ~None~
*** TODO Why does remove_* call ~kevent~ and not add_*?
*** TODO `Ident::Filename` should be `Ident::Filename(Arc<Path>)`
*** TODO Remove `find_file_ident` and use another hashmap to map paths and fd's
*** TODO ~Event.data~ may be negative in some cases

** Non-breaking

*** TODO Try and abstract away ~NOTE_TRACK~ and ~NOTE_CHILD~ if possible and non-breaking
*** DONE ~get_event~ should probably check ~started~ status
*** TODO Make sure that filters and flags are sensible
*** TODO Why does ~as_size~ exist?
*** TODO implement ~timer~ and ~signal~
*** TODO ummm add ~stop~?
*** TODO iterator with a timeout?
*** TODO ~UncheckedWatcher~
*** TODO async api
*** TODO bulk api