Make the manager an expression context
Store the orientation in ActionRunner
Rename the UpdateFunction aliases

Extracts the alias for easier construction.
Implement the Accel action handler
Implement the ChangeDirection action
Implement the ChangeSpeed action
Implement the Fire action
Clean up the Wait action logic
Add some comments for Vanish and Wait
Install bulletml
Support using the build tree as well
Add a top-level module for application use
Export bulletml_elements as well
Remove unnecessary methods from ExpressionContext
Remove unnecessary templating of Resolved
Clean up the BulletManager interface