[Feature Request] Add support for MCP9808 i2c temperature sensor

[yweber]

I bought one of these sensor in order to monitor the internal temperature of a solar node.

Their is an an AdaFruit library for MCP9808.

I've build a firmware with MPC9808 i2c sensor support, and I would be pleased to submit a PR with my patch.

Following the contributing guidelines I'm submitting this issue before creating a PR.

[yweber]

Here is the patch yweber@f98f544