New methods in TTCSSRuleSet to retrieve attributes for Core Text formatting.

- New method <code>paragraphAlign</code> - Return an <code>CTTextAlignment</code> based on the
<code>text_align</code>CSS property.

- New method <code>attributedStringDictionary</code> -
Return an Dictionary with formatted attributes in order to use with
<code>NSAttributedString</code> objects.

- Now accept the <code>font-style</code> CSS property. 

- Implement the <code>NSCopying</code> protocol. 

- New <code>coreTextFont</code> method return an Core Text Formatted Font (<code>CTFontRef</code>) 

- <code>UIFont</code> are created using Core Text formatting. So you can use real <code>bold</code> and <code>italic</code> properties and the class will pick the
correct System Font.