0.6.0

Fixed multiple values support.
You may need to overwrite your tags if you have called the Tag::add_item method with the same key multiple times,
since the spec states that
"Every Tag Item Key can only occures (at most) once".

• Updated byteorder to 1.5.
• Added TryFrom<&Item> trait implementation for Vec<&str> and &str.
• Added TryFrom<Item> trait implementation for Vec<String> and String.
• Removed ItemValue enum and Item.value field; use TryFrom instead.
• Added ItemType { Binary, Locator, Text } enum.
• Added Item::new(key, type, value) method.
• Removed Item::from_binary, Item::from_locator and Item::from_text methods; use Item::new method instead.
• Added Item.add_value method.
• Removed Tag::add_item method; use Item.add_value instead.
• Added Item::with_type method.
• Added Item::with_value method.
• Added Item.get_type method.
• Changed Error enum:
  • Removed: FromUtf8, ParseInt
  • Added: ParseItemKey, ParseItemBinary, ParseItemValue, ParseLyrics3V2SizeStr, ParseLyrics3V2SizeInt.
  • Changed:
    • BadItemType -> InvalidItemType(u32).
    • BadTagSize -> InvalidTagSize.