Adds a vimap_fold convenience class to ext

This should make it really easy to do vimap parallel map + fold
operations
Split up the vimap_fold into a runner and a vimap_fold interface
Feedback from code review

Fixed up placement of some functions, added docstrings, and made the test
data better.
Bump version to 0.1.7
Updating file_runner

Now it uses argparse instead of optparse and has different serialization
options for the output
Just use print if there is a serializer

This makes the output valid json
Merge pull request #23 from jolynch/master

Adds a vimap_fold convenience class to ext