New API views that respond with JSON.

Created a new API.py view that responds with JSON for client-side
scripting. Currently, API has three functions:

sections - list of publicly available sections. Accessed through
    /API/json/sections
latest_articles - list of publicly available articles, sorted
    newest first. Accessed through /API/json/latest
article_json - a dictionary containing the requested articles
    properties such as title, body, decription, etc. Accessed
    through /API/json/article/<article_pk>

The JSON responses contain the following keys:
    domain - string, http://site_domain/
    success - boolean, for evaluation purposes
    contents - dictionaries or list of dictionaries