Fix golang/go#49219

• Revert backoff v4 for gopath compatibility

• Backoff v4
• Reworked cluster discovery
• Fix rare connection goroutine leak
• More tests

• Fix closing connection pool with uninitialized lazy connection

• Reworked and tested new connection pools with multiple queries per connection
• Socket Read- and WriteTimeout replaced with context timeout
• Mock assert fix
• Connection pool fixed initial size
• Changes added offsets

• Added JSON tags to ConnectOpts to make it serializable
• Blocking mocks for responses
• Fix Connect documentation
• Added Type to ChangeResponse
• Added bitwise operations support
• Added write hooks support

#451 Memory leak was fixed

• Moved to rethinkdb organization
• Renamed to rethinkdb-go repo
• Renamed to rethinkdb package
• Fixed instability integration tests due to same tables names
• Fixed wrong asserts in integration tests

Fixed

• Rare Connection leaks if socket errors occurred
• Updated ql2.proto file from rethinkdb repo

Added

• Support for independent custom type marshalers

Fixed

• Connection work with sockets, now only a single goroutine reads from socket.
• Optimized threadsafe operations in Connection with channels and atomics instead of mutex.
• All tests with real db moved to integration folder

Added

• Added support for tracing with opentracing-go
• Added a brand-new unit tests for Connection