Manage per-screen status bars.

Provides a few helper functions to manage per-screen status bars while dynamically responding to screen changes. A startup action, event hook, and a way to separate PP styles based on the screen's focus are provided:

• The dynStatusBarStartup hook which initializes the status bars.
• The dynStatusBarEventHook hook which respawns status bars when the number of screens changes.
• The multiPP function which allows for different output based on whether the screen for the status bar has focus.

The hooks take a DynamicStatusBar function which is given the id of the screen to start up and returns the Handle to the pipe to write to. The DynamicStatusBarCleanup argument should tear down previous instances. It is called when the number of screens changes and on startup.