message: feat(header): add ContentType::xml() constructor
diff: @@ -68,12 +68,18 @@ impl ContentType {
  ContentType(mime::TEXT_PLAIN_UTF_8)
  }
  - /// A constructor to easily create a `Content-Type: text/html; charset=utf-8` header.
  + /// A constructor to easily create a `Content-Type: text/html` header.
  #[inline]
  pub fn html() -> ContentType {
  ContentType(mime::TEXT_HTML)
  }
  + /// A constructor to easily create a `Content-Type: text/xml` header.
  + #[inline]
  + pub fn xml() -> ContentType {
  + ContentType(mime::TEXT_XML)
  + }
  +
  /// A constructor to easily create a `Content-Type: application/www-form-url-encoded` header.
  #[inline]
  pub fn form_url_encoded() -> ContentType {
  