Misc changes / cleanup before v0.1

[cdeil]

This pull request contains some misc changes and cleanup I'd like to make before releasing v0.1:

• [x] Don't expose hips.utils in the public docs. Make it simple for end-users and expose everything they should know about in the top-level hips namespace. The one thing from hips.utils that they need is WCSGeometry, which I import into the top-level hips namespace.
• [x] Shorten the docs landing page, move the content to a new "about" page.
• [x] Update drawing description to what we do in the code (e.g. projective transform, not affine transform with triangles)
• [x] Update getting started guide to include a color image draw example.
• [x] Misc code, test and docstring cleanup

@tboch - Do you want to review this today or are you already on vacation?

[coveralls]

Coverage increased (+0.3%) to 97.662% when pulling 0259b78bbc7ea75fecd15bd63b21334c6f1edc4c on cdeil:misc-cleanup into 0dcbe516a812ffc2e351f697fd5ab08915f43757 on hipspy:master.

[cdeil]

@tboch @adl1995 - I've added an "about" page, and updated the "drawing algo" page and done other docs changes. If you have time to review them now, please do. Otherwise I'll merge after lunch and then you can still review and comment in the coming days of course!

[cdeil]

I've added an example drawing jpg from Fermi color to the high-level docs.

The result is bad:

I've never seen a successful RGB draw, and I don't know yet what the issue is. @adl1995 - Have you made any progress on that yet?

If no, I would like to merge this PR after lunch, and then work on this issue in the afternoon.

[tboch]

@cdeil sorry, I'm already off

[coveralls]

Coverage decreased (-0.7%) to 96.692% when pulling b4e045e67389cf82836dfdc2f80752941325ad16 on cdeil:misc-cleanup into 0dcbe516a812ffc2e351f697fd5ab08915f43757 on hipspy:master.