Solarposition integration

I've tried to make this ```solarposition.py``` and ```location.py``` PR as small as possible. I believe that it almost cleanly integrates with master, but I have not tested it extensively since I do not know the status of the test suite. I added a couple of test modules for my new modules as well.

The primary reason why this PR would be incompatible is that in order to make it python3 compatible I had to nuke the ```__init__.py``` imports. I could have updated them to be python3 compatible but it sounded like we likely to remove or significantly update them anyways.

My ```solarposition.py``` requires my version of ```location.py``` (IANA/pytz timezones). Since these two files can be added without breaking anything, I stopped here. Further integration would require us to commit to changing the tz spec. As mentioned elsewhere, I'll try to help with the TMY problem so that we can move forward with this.

I made extensive but mostly cosmetic edits to ```pvl_ephemeris.py``` before the new cythonized code was available. My ```solarposition.py``` requires my ```pvl_ephemeris.py``` for tz handling.

```pvl_tools.py``` had some indentation issues that python2 allowed but python3 did not. I've seen lots of indentation issues in other modules too.