Ndsampler

Added

* New method `load_target_annots` that just finds overlapping annotations

Added
* `load_sample` now takes an `annot_ids` argument to skip the spatial lookup
and use something precomputed.

* Can now specify `optimize=False` in `load_sample` target dictionary to
prevent delayed image from doing any optimization.

Added
* Experimental support for `rtree` in `isect_indexer`
* Add `verbose_ndsample` option to the target dictionary for debugging

Changed
* Small speedups

Added
* Add CocoSampler.coerce

Fixed:
* Work around issue in delayed image where it is not handling interpolation
correctly.
* Fixed np.int, np.float, np.bool