Connection Pooling, API Improvements & Bug Fixes

• Replace sliver with pluggable idStrategy approach
• Update mutate to always return document (changed or not)
• Make _indexes available during mutate
• Remove deprecated progress support from promises
• Add default timeout to ensure promises reject on connection failure
• Use whistlepunk for logging
• Add ability to specific # of connections per node to start with in the pool
• Bug fix - connection pool doesn't cycle connections per node correctly
• Bug fix - correct how defaults are applied to node settings
• Introduce custom errors for bucket operations (get, put, mutate)
• Include docs after multi-get operations
• Simplify and clean-up log entries
• Update/Cleanup README