Trail spec page

This is a v1 page for the trail data spec. It will be updated regularly over the next week or so, but we want to provide a publicly accessible URL as soon as possible (mid-day Thursday April 10 if at all possible).

- An "opendata" directory was added, with "trails" added as a subdirectory. This page lives in that subdirectory as index.html.

- Media assets on this page, if not already hosted elsewhere, have been added in a new "trails subdirectory which can be found in media/images/trails. This can be changed at the pleasure of the tech team.

**Future Improvements**

I ended up cutting out quite a bit from this version of the page, and quite a few updates will need to be made before we formally issue a Request for Comment. Those include:

- Publish the draft blog post through the conventional blog workflow, and preview the post on the Trail Spec Page, rather than hard-coding the text here.
- Create separate pages for each table of the specification, a lá GTFS.
  - Add top-level narrative description to each table
  - Link to Google Document that serves as working copy of the spec.
- Use Wufoo to collect form submission (to be created with @jmadans).
- Include distinct Calls to Action for different audiences (Learn more, download sample data, pitch your park district, etc.)
- Add additional "Advisors" before launching the Request for Comments Period.
- Perhaps allow visitors to RSVP to join the promoted conference calls?
- Include links and expository copy for any validators, transformation scripts, or other ETL assets that may be developed.
- Responsive layout improvements for tables and code snippets.
- Sundry other enhancements.

**Outstanding Questions**

- What is the best approach for hosting sample data for download?
- Am I doing this right from a workflow perspective? I certainly found the Jekit tool to be pretty handy.