add @length attribute: number of bytes of a binary part or a text part encoded in UTF-8 (i.e. not the original lenght in the MIME message)
0d3eb5129582878ca800b5ab3241d5f2907a3eb9 v0.13
accf73de67786d37297a509ff6ce65c99d6e5c0d v0.14
8730e2d0db0e866da5327d6a73a9c82ec23a96b0 v0.15
b70e616178c064c7a296147e3787c853326c5898 v0.16
afeb4e096753e12a89ecf07964e5458706759915 v0.17
798dfcded2f57c1c662e881f0d5d6f58929bfe4a v0.17.1