Stage #1 of core breakup: move everything under lib

BUILD

Makefile

binding.gyp

build.yaml

config.m4

gRPC.podspec

grpc.gemspec

package.json

package.xml

src/core/lib/census/README.md

src/core/lib/census/aggregation.h

src/core/lib/census/context.c

src/core/lib/census/grpc_context.c

src/core/lib/census/grpc_filter.c

src/core/lib/census/grpc_filter.h

src/core/lib/census/grpc_plugin.c

src/core/lib/census/grpc_plugin.h

src/core/lib/census/initialize.c

src/core/lib/census/mlog.c

src/core/lib/census/mlog.h