feat(header): add ContentType::xml() constructor

Author: spk

src/header/common/content_type.rs

@@ -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 {