Represents a multipart HTTP message body, parsed according to the syntax of RFC 2046.
Of particular interest to HTTP are `multipart/byte-ranges` and `multipart/form-data`,
Although the headers of a Multipart body part will contain the full headers from that body part, libsoup does
not interpret them according to MIME rules. For example, each body part is assumed to have "binary" Content-Transfer-Encoding, even if its
headers explicitly state otherwise. In other words, don't try to use Multipart for handling real MIME
multiparts.