Release 0.3.2

Added

• Added new(), clear(), empty(), is_empty(), len(), push(), push_bytes(), push_str(), as_bytes(), as_mut_bytes(), into_bytes(), and to_bytes() to http::UnpackedResponseBody
• Implemented Add and AddAssign functionality for http::UnpackedResponseBody: &[u8], &[u8; N], and &str
• Implemented AsRef, AsMut, Clone, Default, and Write for http::UnpackedResponseBody
• Implemented a range of From conversions for http::UnpackedResponseBody: &str, &mut str, String, &String, Box<str>, Cow<'a, str>, char, and u8