Option to use @property tag for variable definitions. [Important for YUIDoc]

Added a single option for the package to use @property tag for the variable definition instead of @type tag, which is used by default.

This is crucial for YUIDoc documentation tool, since it only recognises definitions that have one of the primary tags:
@module, @class, @method, @property, @event

Currently DocBlockr has option to add @method tag to function declarations which is perfect for YUIDoc.

This patch adds the same functionality for variables.

And thank you so much for creating such a great tool. It is very nicely programmed and works amazingly.
Developing your code is also a pleasure.
Cheers, Nazar.