Add CLI support for testing textual description of locations

This feature should support the following usage(s):
* High-level, low-to-medium detail textual descriptions:`lein describe x y`
* Low-level, high-detail: `lein observe x y`
* Everything known about the given pixel (i.e., using all map layers) should be provided in human-readable text
* Should the `OBSERVE` command include surrounding pixels?
* Or should there be a third, bird's-eye command?