Content-types

- Changes .js back to text/javascript
- Adds a few new types
- Adds comparison to builtin mimetypes

Added [py.typed](https://github.com/mikeckennedy/content-types/blob/main/content_types/py.typed) file to suppress mypy typing warnings. Thanks sanders41 Available on PyPI now.

Adds many more file extensions as known types.

Initial public release.