Build User Guide for v1.4 from Docs folder

[justingeeslin]

With the new 1.4 release, we should think about a User Guide for this release, and every subsequent release.

The vision:

• Built from community-maintained markdown files
• Includes bookmarks, like the original. Great idea for a PDF so large

[justingeeslin]

My initial plan of attack is to move the current User Guide into the docs Jekyll site, then use something like wkhtmltopdf to transform that into a PDF.

[justingeeslin]

Practicing the PDF to Markdown conversion with #51; will move the tutorial before the entire User Guide.

[justingeeslin]

I've created an Markdown version of the User Guide. Thank goodness for pandoc. This is currently kept in the feature branch feature/user-guide-html.

There's still a lot of work to do before this is ready to convert into a new PDF, but that's the goal.