set_font_options
Description:
Sets the new font options for this.
The Backend will copy the FontOptions.
If options is null, the first following call to 
      get_font_options will return the default font options for 
      this.
This function is intended for actors creating a Pango layout using the PangoCairo API.
Parameters:
| this | a Backend | 
| options | Cairo font options for the backend, or  |