Turn docs into stand-alone site with a useful nav structure

GH Pages themes are nice but have 2 limitations that I think require us to find a different solution:
1. The default supported Jekyll themes don't have any nav structure
2. CoA docs/guidelines belong on a city-controlled domain, not on a `GitHub.io` subdomain.

Installing and configuring a Jekyll theme is easy. I've already done it using [the prototype Zilker theme](http://github.com/cityofaustin/zilker-theme) that Jake scaffolded a couple of months ago, and deployed as a static site via [Now](https://zeit.co/now). The real trick is identifying a hosting and DNS scheme that allows us more flexibility than what we currently have with AustinTexas.gov.

@amenity is running into the same issues I am with this stuff so we're trying to identify the right person to talk to about DNS policy, subdomains, and cloud hosting.

Start by reviewing the prototype Zilker theme and the current AustinTexas.gov constraints described in the issue, then clarify the DNS, subdomain, and cloud-hosting requirements with the named stakeholders. Done means an agreed hosting and DNS scheme supports a stand-alone docs site with useful navigation on a city-controlled domain.

Written by the indexing model from the issue text.