Add some tests

[EdGrrr]

As the title says...

[EdGrrr]

Now includes some tests based on the LibRadTran tests. These are not all working yet, but the main issues now are

• Do not include zout in the output_user option
• The code for parsing output files where varying scattering/observation angles are used doesn't work for cases where uu is not in output_user. At the moment it just limits the use of these tests directly, so is not a high priority to fix

https://github.com/EdGrrr/pyLRT/blob/4e315427d0c22183ba1cd0fdb81da3975c9bdb60/tests/test_RadTran.py