Fix error with the reference docs not being rendered

[Tinitto]

Why

The reference docs were not showing up in the docs site
Fixes #32

What was Done

• Changed the "all" declarations in the subpackages to be a list of strings instead of classes and modules
• Added the "syncio" and the "asyncio" modules to the reference.md page explicitly
• Added the headings for each module in the reference.md page

How to Test

• Clone the repo

git clone git@github.com:sopherapps/pydantic-redis.git

• Install dependencies

cd pydantic-redis
python -m venv env
source env/bin/activate

• Serve the mkdocs site

mkdocs serve

• Visit the http://127.0.0.1:8000/pydantic-redis/reference in your browser