Add more tests to galois_16

[darrenldl]

Certain functions are missing direct tests, not overly urgent atm however, so best to focus on development of new code first.

[darrenldl]

Moved to 4.0.1 release to allow release of 4.0.0 sooner.

galois_16 doesn't seem to be missing too many tests if any, so will come back to this in a later release.