Kiss-headers

*Changes :*

- **Bugfix:** Function `is_legal_header_name` approved some illegal header name. 41
- **Miscelaneous:** Added MANIFEST.in file
- **Other:** Method `values()` of the class `Headers` was returning `NotImplemented`, now raise `NotImplementedError` instead.

*Changes:*
- **Bugfix:** The double-quote character wasn't handled correctly inside an attrs value.
- **Bugfix:** Cannot pass a BufferedReader (fp) to the parse_it function.
- **Bugfix:** Fix the unfolding inside header content.

*Changes:* This is a bugfix release. (36)

- **Bugfix:** __gt__ and __lt__ implemented but missing __ge__ and __le__ in Header.
- **Bugfix:** Attributes.remove() method would fail to remove properly if with_value is None and index is not provided.
- **Bugfix:** Support negative index in Attributes.insert() method.
- **Bugfix:** Delete an attribute no longer remove members that are named after the target key. 35
- **Improvement:** Docstring additions.

This is a bugfix release. See PR 34

*Changes:*

- **Improvement:** Implement insert() method on Headers class.
- **Feature:** Introducing the `Attributes` class in models. Attributes/members are now ordered by default.
- **Improvement:** Add pop() and insert() methods on Header class.
- **Bugfix:** Unescape the double quote char in the cookie value when using SetCokies or Cookie classes.
- **Improvement:** Implement `valued_attrs` property on Header to extract a list of distinct attributes that have at least one value attached to them.

The biggest improvement is that the Header class now acts ordered on its members and attributes/keys/values. See PR 32

The package will most likely go into feature freeze until 3.0-dev. The current focus will be around tests/docs and issues addressed. Enjoy 🎉
*Thank all present and future adopters.*

Docs are going to be updated soon.

**Changes:**
- **Bugfix:** __dir__ method in `Header` instance could contain entries with illegal characters.
- **Documentation:** Major update available at [kiss-headers.tech](https://kiss-headers.tech)
- **Bugfix:** Allow set item value to contain comma-separated entries in `Headers`.
- **Bugfix:** pop() method on `Headers` was discarding output_lock_type() toggle.
- **Feature:** Introducing `index()` method on `Headers` class. Behave like list().index().
- **Bugfix:** `ContentDisposition` was rejecting perfectly valid non-ASCII filename.
- **Improvement:** Add ready-to-use methods in `ContentDisposition` class.
- **Improvement:** Creates py.typed file. 29
- **Others:** Docstring improvements.