Trn 126

The content of the ticket is (https://jira2.iparadigms.com/browse/TRN-126)

Although we don't currently intend to store our response data inside walker, it would make walker far more useful to a broad audience and should greatly help project adoption. It should also be very easy to implement.
Basically:
Add a config flag datastore.store_response_body, false by default
Add a column body to walker.links
If the flag is true, have cassandra.Datastore store the response body in that text column
Since this could be important to others, update the README to note that Walker can do this
Yeah that's a fair point. I'd say just keep it consistent with whatever we have in config.go and walker.yaml. If we do make it more generic as you're saying and change the config key name (from `cassandra` to `datastore` or something) then I think at that point we'd have to go back through and modify relevant comments.