Add a logger module to integrate with Cloud Logging

[jhuleatt]

Create a Python equivalent of the Node logger subpackage to integrate with Cloud Logging's structured logs

Also include trace; https://github.com/firebase/firebase-functions/blob/aae1abd55930550636e8e95c41feefcb617edc9d/src/common/trace.ts#L6

[ekalosak]

Why not just format stdout logging as a valid UTF-8 JSON string? This is what I'm using and Cloud logging picks it up and parses it automatically. I wonder what value an additional module would be?

[exaby73]

@ekalosak #121 does print JSON which is parsed by GCP