Added conversion support for some css properties (convert from xhtml to docx)

Hello!

I needed some features to work when converting from html to docx. So i realized them. Tested on html code i work with:
 - different fonts with css propery font-family;
 - font-size in px;
 - background-color for text and paragraph;
 - [line-through] css property;
 - sub css property for vertical alignment.