v2.6.0

• Added licence type to gemspec #274
• Serialization content type configuration #152
• Add NewRelic category to example #273
• Pass additional global Bunny session configuration #276
• Sneaker.spawn exits with exit_code 1 when no configuration is provided #280
• Added opt-in option for sharing bunny connections for worker group #266
• Bumped bunny version from 2.6.* to 2.7.*. #289
• Relaced thread gem with concurrent-ruby gem #279
• Fixed "stack level to deep" error when trying to serialize the exception object in maxretry handler #308