Relation and multipolygon support

[lukasmu]

This pull request can be considered a follow-up to #76.

I initially started to resolve the merge conflict referenced in the pull request mentioned above. But then I decided to rewrite and optimize the geojson parsing method completely.

Finally I added a test based on real data to make sure that the parsing works correctly.Please note that the example.json file in the tests folder can be opened with any geojson viewer.

[ThomDietrich]

Hey @lukasmu,
great work! Looks really good. I added a few minor comments for discussion. Best!

[lukasmu]

A note on the Travis checks:
For Python 2.7 the error occurs due to differences in pickle functionalities that are solely used in the tests. I don't think this is worth fixing anymore (see https://www.python.org/doc/sunset-python-2)
For Python 3.3 there seems to be something wrong with the Travis config

[ThomDietrich]

Thanks for the latest commit. All my comments are addressed 👍💯

[ThomDietrich]

@mvexel @tbolender @t-g-williams What do you think? Anything holding back a merge soon?
Best!

[tbolender]

Everything looks okay, I just added a small clarification comment.

@mvexel We should remove support for 2.7 since it's going to retire anyway soon..

[lukasmu]

@tbolender @mvexel Is there still anything that I can improve on this pull request? Or did you just not yet have the time to look into it?

[tbolender]

From my side everything is okay. I waited since I wanted @mvexel to have a look at it.

[mvexel]

Sorry guys I've been unavailable.. I'll have a look.