This shouldn't care about `_ENTRIES_PER_BIT` (which is the better name for that) because the better name for `self.num_bytes` is `self.num_entries`.  A lot of the entries/bites stuff was changed in a pinch and the variable name refactoring wasn't quite complete.  I'll add those refactoring changes in a future commit since they seem to be a bit tangential to the spirit of this pull request.