HTTP Interface

Requirements:
- Add the ability for external systems to work with Mockdown through an HTTP REST API.
- Create a simple Sinatra-like library for AS3 as a separate library.
- Access projects at: http://localhost/[project-name]/[document-name].[format]
- Access zipped version of project at: http://localhost/[project-name].zip
- Consider support for real-time collaboration in the future.

Start by reviewing the existing Mockdown project structure and determining where a separate AS3 Sinatra-like library could fit. Define the REST routes for project documents and zipped projects from the URL requirements, while treating real-time collaboration as future work. Done means external systems can access both requested resource forms through the HTTP interface.

Written by the indexing model from the issue text.