Set up CI

[hamogu]

It would be very useful to have a CI run on different systems (at least MacOS and linux, but maybe also some more exotic systems). the CI jobs won't do all the accuracy testing of MARX because that takes far too long, but just run some short test (to be defined). This should include:

• read input fits files (run with ACIS)
• run with HRC
• run with grating
• write a fits file
• check that result is sensible (e.g. photons are not all same location, number of photos is not 0).

A difficulty here is that I plan to align marx more with CIAO and read the CALDB files directly. That means that CI tests need to have CALDB available. Maybe I can define some sub-set for testing purposes only because the full CALDB is prohibitively big for services like travis. Alternativel,y I could try to set up a local system (e.g. docker?) to run those tests locally.

[hamogu]

See https://github.com/Chandra-MARX/marx-test. Some of these are implemented that and any further test discussion is in the issue tracker there. Eventually, some of that might be run in CI in this repro.