Adding python 3.6 to CI builds

[bsipocz]

Probably we need to wait a bit more until all the dependencies become available on python 3.6.

This PR also removes the dependency on standalone wcsaxes package, closing #104.

[cdeil]

@bsipocz - Thanks!

Indeed the Python 3.6 builds fail because Shapely isn't available yet.

The Python 3.3 build is failing because wcsaxes isn't available:
https://travis-ci.org/astropy/regions/jobs/187507998#L493
I'm +1 to just not add a Python 3.3 build.
So far we support Python 3.4+ and clearly state it in setup.py and here:
http://astropy-regions.readthedocs.io/en/latest/installation.html#installation
(I'll file a separate PR or issue to suggest we bump to Astropy 1.3 and use wcsaxes from there.)

@bsipocz - I'm assigning this PR to you. Let us know when this is ready for final review.

[bsipocz]

@cdeil - your suggestions sound good both for dropping 3.3 from the matrix and requiring astropy1.3. I'll come back to this PR in a few days to check whether shapely and mpl are available for python3.6.

[cdeil]

@bsipocz - Is it possible to finish up this PR now? Or are there still things missing for Python 3.6?

(I'd like to make the regions 0.2 release now)

[bsipocz]

@cdeil - I don't think there is any problem with python3.6, we already have a conda package for 0.1 for it with it.
The only reason that this is not yet merged is that shapely is still missing from the default channel. If you think it's OK to use conda-forge for those jobs in the matrix where shapely is required then this will probably get a green status.

[astrofrog]

I think using conda-forge for those cases makes sense

[cdeil]

I think using conda-forge for those cases makes sense

👍

[bsipocz]

@cdeil - I'm having difficulties to make the python3.3 test pass, e.g. https://travis-ci.org/astropy/regions/jobs/201139597#L786
I wonder what are the plans for dropping this version?

[cdeil]

@bsipocz - Let's drop Python 3.3 for testing.

(this issue already came up when you first made this PR and we agreed to drop it, see discussion above).

[bsipocz]

Oops, sorry. I remember that comment, but misremembered that it was in this repo...

[cdeil]

I've moved this under the 0.2 milestone.
It looks like this is almost ready, and I do think Python 3.6 support (ensured via CI testing) and removing the mention / support for the old standalone wcsaxes are important and good changes.
So even if this takes a day or two, I'd prefer to have it in before making the release.

[bsipocz]

@cdeil - Done. Coverage has dropped, I assume only because I haven't rebased this branch.

[cdeil]

@bsipocz - Thanks for this PR and all your work on CI !