Ability to add JSON-like output added.

[dennlinger]

Instead of having to deal with cumbersome XML output, this only outputs the tags (and their information) to the users in a JSON-like object. Aside from Heideltime's added attributes, I further added the temporal tag's text, as well as the absolute character position.

Three pointers that might be important to discuss here:

• Is it clear for users that this will in fact not be JSON (i.e., written as a .json file), and rather just return a Python dictionary?
• Is handling this through the output_type appropriate (instead of adding a separate option)?
• Note that this also introduces additional dependencies, which I am not sure how to best include in the setuptools. I am quite sure there was an option to automatically install them as necessary, will also add this, if wanted.

[dennlinger]

ping @PhilipEHausner: "Rebased" PR as discussed offline.