Major Release

• Added Go Module support
• Dropped support for Go 1.9 and lower
• Implemented Connector interface
• Improved buffering
• Added connection liveness check
• Improved marking of bad connnections
• Updated collations and made utf8mb4 default
• Made mysql.NullTime compatible with sql.NullTime
• Removed support for CloudSQL via appengine/cloudsql

See CHANGELOG.md for full details