Improve batch execute - Githubissues

This PR improves the batch execute API (fix #47)

Rename #execute_multi to #batch_execute. #execute_multi is still available but will be deprecated eventually.
Add support for batch query execution with any enumerable. This can be done with any object that responds to #each.
Add support for batch query execution with a block, or by calling with a callable.

digital-fabric / extralite