Parses <Fixed>

        @param node: Node containing the <Fixed> element
        @type node: xml.etree.Element

def parse_fixed(self, node):
        """
        Parses <Fixed>

        @param node: Node containing the <Fixed> element
        @type node: xml.etree.Element
        """

        try:
            parameter = node.lattrib['parameter']
        except:
            self.raise_error('<Fixed> must specify a parameter to be fixed.')

        try:
            value = node.lattrib['value']
        except:
            self.raise_error("Fixed parameter '{0}'must specify a value.", parameter)

        description = node.lattrib.get('description', '')
        
        self.current_component_type.add_parameter(Fixed(parameter, value, description))