Create initial tests for article results (#16)

Provides automated testing of the article scraper using Instapaper configuration files.

Reading and internal representation of the configuration files is provided by the `saulify.sitespec` module. Site configuration files are stored in the `sitespecs` directory (as opposed to `tests`, as they may also contain article extraction rules that are not specific to testing).

Run the test suite by typing
    
    python runreport.py

in the root directory of the project. The output is a series of JSON dictionaries (one per line) detailing the results of each test.
The only thing that caught my eye about this is that replacing newlines in a Markdown doc might make the plaintext pretty difficult to read. Imagine for example a table (in Markdown) having the newlines stripped; it would look pretty strange. It might be best to use the scraper's plaintext attribute here instead