Release 0.4.0

New features

• Implement a @register_stateful_transform decorator to register new stateful transformations (#85)

Maintenance and fixes

• Fix evaluation of new offset terms with call arguments (#81)
• Multiple calls with unnamed attributes resulted in errors due to trying to hash unhashable types (#88)
• Term names with call components now use the proper lexeme when one argument is a string (#89)
• Detect stateful transformations by attribute instead of name (#90)
• Moved tests out of the formulae directory (#91)
• Use pyproject and improve deployment workflow (#92)