Tattler

- Fix failure to deliver email notification if it's plain-only and contains special characters
- Fix tattler prioritizing old-style template format to new-style if both co-existed

- Add tattler_livepreview to assist template editors with automatic expansion and delivery upon save.
- Rename template files to simplify editing: body and body_plain -> body.txt, body_html -> body.html, subject -> subject.txt, priority -> priority.txt . The old naming is still supported until v3.0, but will log deprecation messages.
- Automatically detect if a common ``_base`` is shared among all scopes, help directly in the template base directory.

- Support sending complex context data using JSON files in `tattler_notify`.
- Support TATTLER_SMTP_TIMEOUT envvar to control SMTP timeout (default 30s).
- Automatically detect when SMTP connection should be TLS based on target port.

- Configure client endpoint programmatically, default to `127.0.0.1:11503`.

- Support running on python 3.9, from good old 2020.
- Support multiple SMS sender IDs.
- Support mobile numbers with '00' prefix when operating without addressbook plug-ins.

- Include new README with screenshots, better description, quickstart, contributing infos and links.
- Add 'user_id' variable to native template context.
- Streamline python package by removing superfluous docs sources, now moved to repo root.