Merge remote-tracking branch 'google/release-0_13' into master-is-14

Makefile

build.yaml

package.json

src/core/surface/version.c

src/csharp/Grpc.Core.Tests/GrpcEnvironmentTest.cs

src/csharp/Grpc.Core/Version.cs

src/csharp/Grpc.Core/VersionInfo.cs

src/csharp/build_packages.bat

src/python/grpcio/grpc_version.py

src/ruby/lib/grpc/version.rb

templates/package.json.template

templates/src/csharp/Grpc.Core/VersionInfo.cs.template

tools/doxygen/Doxyfile.c++

tools/doxygen/Doxyfile.c++.internal

tools/doxygen/Doxyfile.core

tools/doxygen/Doxyfile.core.internal