This introduces a new internal package named version to house the
version information and updates the various code to use it. This allows
both dcrd and dcrctl to make use of the package so the version
information only needs to be bumped in one place and also ensure that
any link-time overrides to the pre-release and/or build metadata apply
to both.
Also, while here, include the OS and architecture in the version log at
start of day as well as the output from the version CLI flag.