Changes :
- Bugfix : Better detection of an illegal header name.
- Improvement : parse_it() was too permissive and allowed illegal header name to be included.
- Feature : Reversed can now be called upon an Headers instance.
- Feature : Sorted can be used with an Headers instance to return a list of Header in alphabetical order.
- Bugfix : ContentDisposition custom class was not encoding fallback filename properly.
- Improvement : Headers class can be instantiated like
Headers(Header("Content-Type", "text/html"), Header("Allow", "POST")).