Add base64 decoder

BUILD

Makefile

binding.gyp

build.yaml

config.m4

gRPC.podspec

grpc.gemspec

package.xml

src/core/ext/transport/chttp2/transport/bin_decoder.c

src/core/ext/transport/chttp2/transport/bin_decoder.h

src/python/grpcio/grpc_core_dependencies.py

test/core/transport/chttp2/bin_decoder_test.c

tools/doxygen/Doxyfile.core.internal

tools/run_tests/sources_and_headers.json

tools/run_tests/tests.json

vsprojects/buildtests_c.sln

vsprojects/vcxproj/grpc/grpc.vcxproj

vsprojects/vcxproj/grpc/grpc.vcxproj.filters

vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj

...jects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj.filters