Vitess v2.0.0-alpha3

Changes since v2.0.0-alpha2

• Better PEP 0249 compliance in Python client.
• Type-checking result cursor for Java client.
• VTGate automatically adds annotations for filtered replication.
• All RPC protocols are now off by default, and must be explicitly enabled with the -service_map flag.
  • Previously the BSON protocols were enabled by default, and had to be explicitly disabled in -service_map if unwanted.
• SQL is now consistently represented as a UTF-8 string.
  • Previously it was represented in some places as a byte array.
• Update to gRPC beta.