add checks for many feature combinations

fix #303 (closed)

some crates are not tested because they don't compile with no feature enable, and only check is run, not test, because it's order of magnitude faster, and for many crates, test won't compile without some features enabled.

I think this is good enough for now, the next step would be to fix the things currently ignored, and then to have actual tests run regularly (but probably not on each commit, and probably with handpicked feature combinations. This MR checks close to a hundred combinations in total which would be really slow to compile and test)