Additional commands for all pxm boolean

Right now pxm has bash scripts, python scripts, external python commands and bash functions to assert various things about raster data. All of these methods have slightly different modes of operation (some raise exceptions, some return a special value, some use exit codes, etc) and are not very easy to test.

I'd like to move all the boolean tests from pxm to subcommands of `raster-tester`. Basically anytime we need to ask a yes/no question about a raster or set of rasters, this command should be the place to go.

So far we have
- compare
- isempty

But we could pull in
- aligned
- crosses-dateline
- is_evil
- is_lossy
- validate

This would also give us an opportunity to define and standardize exactly what a Yes/No response should look like and how the bash scripts should handle them
- exit codes
- what gets output to stdout/stderr

Start by reading the existing raster-tester compare and isempty subcommands, then review the current bash scripts, Python scripts, external Python commands, and bash functions that implement aligned, crosses-dateline, is_evil, is_lossy, and validate. Define consistent exit-code and stdout/stderr behavior for each boolean command, then verify that the existing checks can use the standardized responses.

Written by the indexing model from the issue text.