Added proper font-weight and font-style handling with @font-face rule.

This change fixes some issues when specifying a specific font-style or
font-weight through @font-face. For example, when importing a special font
resource specifically for the italic font-style, the PDF output would not
match the correct font if the css rule specifies the style/weight.
Merge pull request #69 from habermann24/font_style_fix

Added proper font-weight and font-style handling with @font-face rule.