Add logging functionality

[jthomerson]

Probably something similar to https://github.com/jeremydaly/lambda-api#logging

[yokuze]

We decided that the standard log object will include these fields:

• level
• msg
• data

When the log level is debug, or something more verbose like trace, then these fields are also added:

• timer - the time, in milliseconds, since the start of the Lambda function request
• remaining - the time, in milliseconds, left until the Lambda function times out
• int - Interface. The type of Lambda event that triggered the request. One of APIGW or ALB

Here are some other fields we considered, but decided were not necessary or that we won't add at this time:

• time / id - not needed because they’re in the CloudWatch output
• function - not needed because each function (typically) has its own log stream
• memory - not needed because it’s logged in the execution report
• route / method - come back to this later
• sample - we can revisit when we add sampling (Consider adding support for sampling to logger #26)

[yokuze]

This was added with #27