Changes:
* I add postgres_databaseutils_test.go for containing all utilities for mocking the database.
* I put appName as a required parameter passed to the New() since it is needed to form the namespace column name.
* I add GetMaxInterval() since it might be needed by the consumer and the test.
* I move the SQL string package variables directly into the function that need it so we could avoid maintenance nightmare in the future.
Major changes:
* Remove intermediate batching of kinesis records
* Call the callback func with each record
* Use functional options for config
https://dave.cheney.net/2014/10/17/functional-options-for-friendly-apis
Minor changes:
* update README messaging about Kinesis -> Firehose functionality
* remove unused buffer and emitter code
