0.31.0

Added an all_columns method, to make it easier to retrieve all related columns when doing a join. For example:

await Band.select(Band.name, *Band.manager.all_columns()).first().run()

Changed the instructions for installing additional dependencies, so they're wrapped in quotes, to make sure it works on ZSH (i.e.
pip install 'piccolo[postgres]' instead of pip install piccolo[postgres]).