Make tests work from installed package via test() function

This includes adding the regression output as a configured
data file and refactoring the test script so it can run
as main to generate the regression data or as a pytest
or nosetest file to run the test.  Also added a simple test()
function that can be run as:

 Ska.engarchive.test()
 Ska.engarchive.test('-s')  # provide intermediate output
Update version to 0.22.1

(This actually happened in the previous squashed commit, so
just making this commit for the record).