v0.23.0

Fixes

• Avoid TypeError in Transaction.__repr__ (#703)
  (by @BeatButton in d6eea8e for #703)

• Feed memoryview to writelines() (#715)
  (by @fantix in 359a34c for #715)

• Add sslmode=allow support and fix =prefer retry (#720)
  (by @fantix in 075114c for #720)

• Loosen message test in test_invalid_input (#751)
  (by @musicinmybrain in bc4127f for #751)

• Support readonly and deferrable for non-serializable transactions (#747)
  (by @pauldraper in 5cf4089 for #747)

• Fix asyncpg with Py_DEBUG mode (#719)
  (by @shadchin in a113d90 for #719)

• Fix docs/Makefile and docs/_static/theme_overrides.css missing from PyPI package (#708)
  (by @musicinmybrain in c306068 for #708)