Fix sending null behavor for empty strings, remove testing hardcode, some refactoring of add_batches
Fix handling of non-encodable types (boolean) and add test
correct handling of null values for ALL data types
add ability to selectively send nulls
improve error and timeout handling
Merge pull request #16 from matthew342/master

Fix sending null behavor for empty strings, remove testing hardcode, some refactoring of add_batches