fix: restore makefile commands

[lorenzo-cavazzi]

fix #81

[emmjab]

Questions:

1. So the CI no longer uses the Makefile (when we switched from travis to github actions), but I get that it's still useful to keep the makefile for local builds & tests.

2. The naming conventions on the variables has been updated a bunch in the github actions, and in order to keep this maintainable it might make sense to update them in the makefile as well.

3. Is there a way to run the github actions locally instead? Maybe this question is backwards and we should just run the makefile from the github action.

4. more of a side-note: the multi-step builds haven't been fixed yet in the github actions (i.e. the 2 cuda builds that rely on "base" which is now py3.7); mostly because I can't see any workaround for duplicated code (but I see the Makefile also uses the duplicated codeblock, so maybe that's the way to go...).

[emmjab]

Ok in order to move forward with updating the builds for this repo, I'm going to move forward with merging this! Tested this by building with make all and make <specific extension> locally:

For documentation purposes, things not covered in this PR:

• missing the new julia extension
• variables don't match github actions (will fix in separate PR)
• repo name for dockerhub doesn't match github actions (will fix in separate PR; maybe this naming is better)
• cuda build had issues but expected
• all the other builds were fine