Release v3.0.0

• Introduce builder pattern construction for OpenTok object (#94, #104) Thanks @mukesh-kum!
• Prefer JSON format response while creating an Opentok session (#119) Thanks @juandebravo!
• Add opentok.close() method to prevent leaked file descriptors (#121, #127)
• Update OpenTok REST API URL (#124)
• Use JWT based Authentication header (#113)
• Update JS samples to use latest Client SDK API and best practices (#126, #129)
• Update docs (9230dfe, 366ca65, #128)
• Add OpenJDK 8 to test matrix (#130)