regression_test.py is misnamed

[orion]

I know this has been on the TBD list for awhile, but perhaps now is a good time to actually do it as people are starting to take a look at the project. Probably a better presentation is a Makefile with one or more support scripts written in python.

[edmc-ss]

There is now a Makefile in the repo that is the equivalent of the misleadingly named regression_test.py. It has a number of build targets, but the default (all) is equivalent to what regression_test.py would do both in a Linux (e.g. CentOS) environment and in a cross development environment (e.g. MacOS where there is no ability to build the C submodules).

Note that the Makefile convention has also been added to the two Golang packages in the cstruct and sortedmap repos.