Add a libuv endpoint to the C core, for use in the Node library

BUILD

CMakeLists.txt

Makefile

binding.gyp

build.yaml

config.m4

gRPC-Core.podspec

grpc.gemspec

package.xml

src/core/ext/client_config/client_config_plugin.c

src/core/ext/client_config/connector.h

src/core/ext/lb_policy/grpclb/grpclb.c

src/core/ext/lb_policy/pick_first/pick_first.c

src/core/ext/lb_policy/round_robin/round_robin.c

src/core/ext/resolver/dns/native/dns_resolver.c

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

src/core/lib/http/httpcli.h

src/core/lib/iomgr/iomgr.h

src/core/lib/iomgr/iomgr_uv.c

src/core/lib/iomgr/pollset_set_uv.c