Prepare 1.8.0 release

[rtpg]

Now that this project is under Jazzband, we're going to look at releasing a version of this package that supports current versions of Django under support.

(At the time of this writing, that means having support for 1.11 and 2.1 at least. 2.2 is a stretch goal)

Remaining Todos:

• Finish implementing the Jazzband guidelines (see this issue)
• Get tests passing in 2.1
• Resolve Removed ORGException causes issues when using GeoDjango after 2.0 #205
• Update the readme for the new jazzband-based maintenance mode and supported Django version changes
• Actually do the release