Bullet Core 1.5.0 and Avro converter hooks

This release updates to Bullet Core 1.5.0 with additional features and exposes the various Avro data type fix methods in the AvroBulletRecordConverter so they can hooked into for further configuration. This also adjusts the Avro converter to work with much deeper data structures than the Bullet schema supports. This lets Bullet pull out nested fields using LATERAL VIEW EXPLODE etc and as long as they are workable with in Bullet, it will continue to work.