gddo-server: centralize config and add log package

This change starts centralizing the configuration for godoc.org. In the
future all configuration, including an environment variable and metadata
server check will go through viper.

This change also adds the new logging library I am writing. In the future
all logging will go through this library.

Change-Id: Id0bed0f3a4dc9acb109545db89d6221a182c37fe
Reviewed-on: https://go-review.googlesource.com/34618
Reviewed-by: Tuo Shan <shantuo@google.com>
417 files changed