Merge pull request #653 from quasiben/feature/jenkins_builds

Feature/jenkins builds
Add test for mixed string dataset
Test that Python 3 doesn't let float nans be coerced to ints
No need to convert_objects
Separate chunking and not chunking
Make sure we close files properly
Try tempfile again
Use our own open function
Shorten test a bit
Arg tempfile
Do or do not there is no try
Use our own opener
Move the functionality out
Refactor test_csv
Try plain returning
Give up
more informative comment
Make data a global instead of a fixture
Remove the last of the classes
Last bit of cleanup