Add facility for extensible relay services with direct async calls#716

williampMSFT wants to merge 4 commits intoOpenDevicePartnership:v0.2.0OpenDevicePartnership/embedded-services:v0.2.0from

williampMSFT:user/williamp/es-tad-testswilliampMSFT/embedded-services:user/williamp/es-tad-testsCopy head branch name to clipboard