Also accept Presentation object as input, not only filepath

[markheckmann]

Firstly, thanks for your work! The package works very smoothly. :)

I have one suggestion for improvement:

In order to use TextReplacer class in other projects, it would be helpful if the the initializer took a Presentation object instead of a filepath. Usually, when processing a PPTX file, the replacement is just one of several steps I need to apply. Hence, it might be useful, if the step of loading the presentation was not part of the the class itself or an alternative input, instead if a filepath.