Redis-simple-orm

- Minor patch for typo

- Handling `ModuleNotFoundError` exception when importing `aioredis`

- Add `pyopenssl` as `redis_simple_orm[txredisapi]` requirements.
- Handling `ImportError` exception when importing `aioredis`

- Remove `extended_save` method
- Add `Model.all()` method on model to get all Model data

- `RSO.aioredis` to be `RSO.asyncio`
- Add `all` method on index class
- Remove `aioredis` from README and extra_requires.
`aioredis` can still be used because its API is pretty similar with `redis.asyncio`
- Index `__model__` property should be set early at Model and its Index declaration
- remove `aioredis` v1 supports

- Do not execute pipeline on `Model.save` if `redis` argument is instance of Pipeline