Add ATRF Parameters

[BatchelorJ]

Add ATRF to GDA2020 transformation parameters, new specific functions for transforming between ATRF and GDA2020, added test coverage of these new functions. Resolves #55

[harry093]

Looks good Josh.

One small suggestion, maybe explicitly state that we acknowledge that the transform parameters are identical between ITRF->GDA2020 and ATRF->GDA2020 or we may get queries about copy pasting

[nich0lasbr0wn]

Can you please point me to the example which shows coordinates before and after?

[BatchelorJ]

Under files changed, in the file geodepy/tests/test_transform.py you'll see a code block starting def test_atrftogda2020(self):. This shows the test values used, the transformation functions used and the assert statements saying that the initial values must agree with the computed values to 5e-5 (0.00005m)

[harry093]

@nich0lasbr0wn, the test values used in the code testing the transformations are taken from the GDA2020 tech manual.

All unit tests are automatically run every time some new code is pushed to master and the results are reported. You can see near the bottom of this page 'All checks have passed' with a green tick in front of it, meaning everything is tickety-boo