Aerich

- Support virtual fields.
- Fix modify multiple times. (279)
- Added `-i` and `--in-transaction` options to `aerich migrate` command. (296)
- Fix generates two semicolons in a row. (301)

- Fix syntax error with python3.8.10. (265)
- Fix sql generate error. (263)
- Fix initialize an empty database. (267)

- Fix postgres sql error (263)

**Now aerich use `.py` file to record versions.**

Upgrade Note:

1. Drop `aerich` table
2. Delete `migrations/models` folder
3. Run `aerich init-db`

- Improve `inspectdb` adding support to `postgresql::numeric` data type
- Add support for dynamically load DDL classes easing to add support to
new databases without changing `Migrate` class logic
- Fix decimal field change. (246)
- Support add/remove field with index.

- Improve `inspectdb` and support `postgres` & `sqlite`.