Merge pull request #67 from brendan-ward/master

Enable connectivity = 8 option for shapes
Merge pull request #69 from brendan-ward/master

Increased performance of rasterize
Save file creation keywords args.

These now get stashed in a 'rio_creation_kwds' metadata namespace
so that you can recover the creation kwds (compress, tiled, etc)
of any file.

Closes #53.