Return the message's Content-Type parameters, as a list.
The elements of the returned list are 2-tuples of key/value pairs, as
split on the '=' sign. The left hand side of the '=' is the key,
while the right hand side is the value. If there is no '=' sign in
the parameter the value is the empty string. The value is as
described in the get_param() method.
Optional failobj is the object to return if there is no Content-Type
header. Optional header is the header to search instead of
Content-Type. If unquote is True, the value is unquoted.