Add msgpack-arduino to Arduino Library Manager

[scls19fr]

Hello,

I noticed that msgpack-arduino is available using PlatformIO as it have a library.json and is available at https://platformio.org/lib/show/5646/msgpack-arduino/

but it will be nice if msgpack-arduino could be added to Arduino library manager

According https://github.com/arduino/Arduino/wiki/Arduino-IDE-1.5:-Library-specification a library.properties file is required - and msgpack-arduino have one. But it's not currently in http://downloads.arduino.cc/libraries/library_index.json

Maybe you should register create a new issue using https://github.com/arduino/Arduino/issues?q=is%3Aissue+is%3Aopen+label%3A%22Component%3A+Board%2FLib+Manager%22

Kind regards