Paxter

- Removed encapsulated outermost `<div>` tag from the HTML rendered result
of the Python document authoring mode.
- Added `NormalApplyWithEnv` wrapper which will
additionally provides environment as the very first argument
before the all the positional and keyword arguments of the wrapped function.

- Moved the HTML escape from the visitor into the document element renderers.

- Fixed bug where function `create_unsafe_document_env` breaks
when the input argument for outside environment is not supplied.
- Made all document element classes dataclasses.

- In both Python string authoring mode and Python document authoring mode,
by default `!` and `` will be transformed into empty string and ``
respectively.

- The function `paxter.pyauthor.create_unsafe_env` was renamed to
`paxter.pyauthor.create_unsafe_bare_env`.
- Introduced document python authoring mode
using `paxter.pyauthor.create_unsafe_document_env`.

- No longer allows -expresion text and fragment list within fragment list itself.
- -switch is no longer needed when embedding texts or fragment lists
within the option section of a command.
- Single symbol command (such as `` and `,`) are now its own node type.