Initial documentation push for halite, updates to 0.17 release notes, updates to hacking guide.

This commit includes the initial push to the main repo for the halite application. As of now the docs are incomplete, however they walk users through the basic setup to get the service running and reduce confusion. Additionally this commit includes links from the 0.17 docs to the new documentation, clarification that halite is not included with the salt-master by default, and that it must be downloaded from pypi. This commit also adds a simple section to the hacking documentation regarding how to preview the documentation after it's been built with Sphinx.