Merge github.com:grpc/grpc into optionalize_client_config

Makefile

README.md

include/grpc/grpc.h

include/grpc/impl/codegen/grpc_types.h

src/compiler/csharp_generator.cc

src/core/ext/client_config/subchannel.c

src/core/ext/resolver/sockaddr/sockaddr_resolver.c

src/core/lib/iomgr/ev_poll_and_epoll_posix.c

src/core/lib/iomgr/ev_posix.c

src/core/lib/iomgr/ev_posix.h

src/core/lib/surface/server.c

src/cpp/server/server.cc

src/csharp/Grpc.Core/CallInvoker.cs

src/csharp/Grpc.Core/ClientBase.cs

src/csharp/Grpc.Core/DefaultCallInvoker.cs

src/csharp/Grpc.Core/Grpc.Core.csproj

src/csharp/Grpc.Core/Internal/InterceptingCallInvoker.cs

src/csharp/Grpc.Core/Internal/UnimplementedCallInvoker.cs

src/csharp/Grpc.Examples.MathClient/MathClient.cs

src/csharp/Grpc.Examples/MathExamples.cs