Flask-migrate

- Regression from 438: check `g.x_arg` exists before accessing it [541](https://github.com/miguelgrinberg/flask-migrate/issues/541) ([commit](https://github.com/miguelgrinberg/flask-migrate/commit/7e8032c61e5c47f4e50b03dcf98c3b20dd5a8e55)) (thanks **Skye Im**!)

- Accept `-x` options for all db commands [438](https://github.com/miguelgrinberg/flask-migrate/issues/438) ([commit](https://github.com/miguelgrinberg/flask-migrate/commit/6f3f889c36030134f87dc1db327c2385d873a4d6))
- Add `--purge` flag to the `stamp` command [540](https://github.com/miguelgrinberg/flask-migrate/issues/540) ([commit](https://github.com/miguelgrinberg/flask-migrate/commit/af67bb093df5652c867b88880c5934bfc68313cc)) (thanks **Jono N**!)

- Compatiblity fixes for Flask-SQLAlchemy >= 3.1 [526](https://github.com/miguelgrinberg/flask-migrate/issues/526) ([commit](https://github.com/miguelgrinberg/flask-migrate/commit/f562178bbe1912912f3cb6877cbae8b0899c74da)) (thanks **David Lord**!)
- Allow `process_revision_directives` option to be configurable [523](https://github.com/miguelgrinberg/flask-migrate/issues/523) ([commit](https://github.com/miguelgrinberg/flask-migrate/commit/821e37fcc4a5e339f197153cdbb4dd2316cbd44b)) (thanks **llc**!)
- Stop testing Python 3.7, as Flask-SQLAlchemy 3.1 stopped supporting it ([commit](https://github.com/miguelgrinberg/flask-migrate/commit/8d175193f00bf4e5578f0142d011093d8cd53d57))

- Correctly obtain database URL with SQLAlchemy 2.0 [505](https://github.com/miguelgrinberg/flask-migrate/issues/505) ([commit](https://github.com/miguelgrinberg/flask-migrate/commit/c8cd02c5d3d43bbab462b863db5417b5d69228bb))

- Remove legacy __future__ import in Alembic templates [504](https://github.com/miguelgrinberg/flask-migrate/issues/504) ([commit](https://github.com/miguelgrinberg/flask-migrate/commit/7a388cfe320254735f4ed65ac655caaf0cae8b28)) (thanks **Pamela Fox**!)
- Add SQLAlchemy 1.4 and 2.0 to the test matrix ([commit](https://github.com/miguelgrinberg/flask-migrate/commit/7a725f2e3267f1c3bb4920cd3bff3a9ff1d7eb6e))
- Switch to pytest as test runner ([commit](https://github.com/miguelgrinberg/flask-migrate/commit/5acd794048d050f85b5dea93052f96abd8a583f2))

- Support "check" command [502](https://github.com/miguelgrinberg/flask-migrate/issues/502) ([commit](https://github.com/miguelgrinberg/flask-migrate/commit/1a893b4fca280f82b1aada6458b7c866c6d3c953)) (thanks **Masamitsu MURASE**!)