Try to load @filename. If there is no loader for @filename's filetype, 
    return @default.

def load(filename, default=None):
    '''
    Try to load @filename. If there is no loader for @filename's filetype, 
    return @default.
    '''
    ext = get_ext(filename)
    if ext in ldict:
        return ldict[ext](filename)
    else:
        return default