Adds new argument --style to direct docformatter to wrap long parameter descriptions that exceed wrap length. Only "Sphinx" style parameter lists are recognized. NumPy and Google style parameter lists still result in existing behavior of not wrapping the long description (this PR sets the framework to add those styles).

Sphinx style parameter lists are in the format:

:param str arg1: A string argument.
:param int arg2: An integer argument.
:return something_good: The return value.
:rtype: bool

This PR will be merged following release of v1.7.0.

Closes #58
Closes #68