Updates README
First draft of the quickstart guide
Returns 400 if the user tries to create two corpora with the same name
Fixes broken tests after Mongodict update

Mongodict now pickles the object before adding it to the database (which I'm
still not sure if is a good idea). I changed the tests to use the Mongodict API
instead of inserting directly to the database.
Merge branch 'bugfix/duplicate_corpus' into develop
Warns the user about the 'no duplicate corpora names' rule in the quickstart guide
Extends the quickstart guide to show the properties list

This also includes an example on how do download the freqdist for a document.
Changes quickstart guide from markdown to rst

This means we use only one markup language for our documentation.
Fixes bug in quickstart code
Adds a link to the quickstart guide in the README file
Merge branch 'feature/tutorial' into develop