Release notes for 509

Add APIs to override built-in terrain material appearance.

tostring() now uses a new cross-platform number formatting implementation that produces precise, round-trippable, shortest decimal output and does this 10 times faster than our old implementation depending on the platform and the input number.

Script analysis now warns about adding new properties to tables exported from a module.

Fixed a bug where the target orientation wasn't being properly updated when it was set from a script.