Cleanup
* ScanMeta should be a lambda
* Delta needs a different primitive `Delta { abs: i64, step: i64 }`
* this will allow for cleanup/removal of all the special case abs code in writer etc
* Need to have distinct cursors for Rle<u64>, Rle<Option<u64>>, Rle<String>, Rle<Vec<u8>>
* maybe get_ref(), iter_ref() for things that implement Borrow()
* would be nice to get rid of all the Cow's
* need more methods to make these behave like Vec such as col[a..b] as a stand-in for
col.iter_range(a..b)
* need to normalize all the min/max stuff - not needed for all slabs and taking up space
* would be nice to have a stat_collector for iter()/get()