Datadog exporter + bug fixes

Fix maxHeaderBytes env variable name + linting fix (#415)

* Fix maxHeaderBytes env variable name + linting fix

* fix key-set tests

[pubsub/gcp] Expose PublishSettings

PR #239 - Expose GCP PubSub PublishSettings to Gizmo users

[server/kit] Properly logging panic messages

v1.3.4

Log the panic message even if it's not of type error (#237)

[pubsub/aws] fixing WithMessageAttributes typo from prior release

v1.3.3

fix typo in the MessageAttributes method (#236)

[pubsub/aws] Adding WithMessaggeAttributes for SNS

Allow to set SNS Message Attributes via context (#235)

* Allow to set SNS Message Attributes via context

* use private context key as suggested by @jprobinson

[observe + server/kit] adding support for Google Cloud Run

Detect cloud run for stackdriver logging (#234)

* Added cloud run detection

* Refactored GetServiceInfo, added Run resource type

* Removed debug code

* Updated docs

* Updated naming to be more clear

* Updated readme

* Renamed func

Adding auth/gcp.Authenticator, rearranged server/kit.Server's logging stack

[auth/gcp] Adding basic google web auth flow capabilities (#231)

* initial WIP

* removing IAM verifier, cleaning up verify logic

* docs

* hooking in custom exception func

* renaming file

* removing unneeded client

* ensuring cookie is cleared

* cleaning up var declarations

* fixing the logger

* Forbids instead of redirecting

* cleaned up verify logic

* state cleanup

* simplifying logic

* avoiding a verify of an empty token

* adding some initial authenticator tests, callback still needs coverage

* adding some callback tests

* making notes in README

[server/kit] adding `HTTP_ADDR` configuration

add http listen addr to config (#230)

* go fmt

* add HTTPAddr to config to allow configuring listen address

[server/kit] Adding leveled logging formatters

[server/kit] Adding log "format" functions that mimic `appengine/log`…

… (#229)

* tidying up example deps

* adding log*f funcs for the kit server

* variable firx

* adding more test logging

* DRY-ing things up a tad

Cleaning up example modules + updating go-kit to v0.9.0

tidying up example dependencies + updating go-kit (#227)

* tidying up example deps

* updating go-kit

* also updating example go-kit