Add new sound assets
Allow world scripts to play arbitrary sounds
Introduce counter world objects
Introduce named counters
Performance tuning
Store color in counter and darken it to distinguish it from the player
Add pwsound levels
Link pwsound to introworld5
Require pwsound completion to access good ending
Use world foreground to color timer

This fixes a bug where worlds with draw triggers could set the color of
the timer.
Play portal spawn sound the first time the player enters introworld4 with the win condition met
Draw message after world script draw trigger