Closes the CHM archive.
        This function will close the CHM file, if it is open. All variables
        are also reset.

def CloseCHM(self):
        '''Closes the CHM archive.
        This function will close the CHM file, if it is open. All variables
        are also reset.
        '''
        if self.filename is not None:
            chmlib.chm_close(self.file)
            self.file = None
            self.filename = ''
            self.title = ""
            self.home = "/"
            self.index = None
            self.topics = None
            self.encoding = None