Documenteer for LSST Science Pipelines (stack) documentation

The LSST Science Pipelines is an EUPS-managed stack. Documenteer includes specific command-line tools and Sphinx configurations to build documentation for both multi-package stacks (such as pipelines.lsst.io) as well as individual or stand-alone stack packages (such as astro-metadata-translator.lsst.io). Documenteer also includes Sphinx extensions to help document domain-specific topics, such as LSST Tasks.