v2.0.0

• [#24] added 64bit event numbers support
• [#22] added current_version to WriteEventsCompleted message and exposed stream, expectedVersion and currentVersion fields in WrongExpectedVersionException class
• added EventStoreBuilder.connectionName(...) method that allows to set client connection name
• added SubscriptionBufferOverflowException - more specific exception for subscription drop cause when 'client buffer too big'
• removed expected version value wrapper ExpectedVersion.of(...) - now simply use expected version number
• renamed class OperationTimedOutException -> OperationTimeoutException
• renamed class HttpOperationTimedOutException -> HttpOperationTimeoutException
• changed enum SystemEventType -> class SystemEventTypes with string constants
• bumped netty version to 4.1.13.Final
• bumped gson version to 2.8.1