Avoid LabelIsNotAscii spam when used with mdns

Make the data integrity check how the data is interpreted;
the check is for ascii only, but we can deal with UTF8,
so relax a little and allow that.

refs: dylanmckay/mdns#13

src/error.rs

@@ -51,7 +51,7 @@ quick_error! {
             display("class {} is invalid", code)
         }
         /// Invalid characters encountered while reading label
-        LabelIsNotAscii {
+        LabelIsNotUtf8 {
             description("invalid characters encountered while reading label")
         }
         /// Invalid characters encountered while reading TXT

src/name.rs

@@ -72,8 +72,8 @@ impl<'a> Name<'a> {
                 if parse_data.len() < end {
                     return Err(Error::UnexpectedEOF);
                 }
-                if !parse_data[pos+1..end].is_ascii() {
-                    return Err(Error::LabelIsNotAscii);
+                if from_utf8(&parse_data[pos+1..end]).is_err() {
+                    return Err(Error::LabelIsNotUtf8);
                 }
                 pos = end;
                 if parse_data.len() <= pos {