I see two options here. I tend to recommend the second option though since this is well documented. This does restrict you to using KV store collection though; CSV files are difficult to interact with via a REST API (I had to write my own in the Lookup Editor to make CSVs editable).
Here are the details:
Using the REST APIs in the Lookup Editor
The REST APIs for the Lookup Editor aren't well documented since I hadn't designed them for use outside of the app itself.
They can be used outside of the app if you want though. The REST handler is here: https://github.com/LukeMurphey/lookup-editor/blob/master/src/bin/lookup_editor_rest_handler.py. You can see an example of how the handler is used by looking at the Javascript here: https://github.com/LukeMurphey/lookup-editor/blob/master/src/appserver/static/js/views/LookupEditVie....
Use the Splunk KV store collection APIs
Alternatively, you can just use the KV store APIs included in Splunk. You can see them here: http://dev.splunk.com/view/webframework-developapps/SP-CAAAEZG
