Aerich

- Refactoring migrate logic, and this version is not compatible with previous version.
- Now there don't need `old_models.py` and it store in database.
- Upgrade steps:
1. Upgrade aerich version.
2. Drop aerich table in database.
3. Delete `migrations/{app}` folder and rerun `aerich init-db`.
4. Update model and `aerich migrate` normally.

- Fix windows support. (46)
- Support `db_constraint` in fk, m2m should manual define table with fk. (52)

- Raise error with SQLite unsupported features.
- Fix Postgres alter table. (48)
- Add `Rename` support.

- Fix tortoise ssl config.
- PostgreSQL add/drop index/unique.

- Fix postgres drop fk.
- Fix version sort.

- Fix bug in windows.
- Enhance PostgreSQL support.