Returns a flag indicating if a given block of MultiMarkdown text contains metadata.

def has_metadata(source, ext):
    """Returns a flag indicating if a given block of MultiMarkdown text contains metadata."""
    _MMD_LIB.has_metadata.argtypes = [ctypes.c_char_p, ctypes.c_int]
    _MMD_LIB.has_metadata.restype = ctypes.c_bool
    return _MMD_LIB.has_metadata(source.encode('utf-8'), ext)