Add IO derivatives of the play, simulate, and animate actions

[Thomas DuBuisson]

I propose we generalize the animate, simulate, and play actions by providing variants allowing IO actions for world stepping and rendering.

The reasoning here is: 1) World-stepping should be permitted to be IO because there might be outside influences on the world state (ex: a networked game). 2) Rendering the world should be permitted to be IO because there might be outside information needed (texture loading, map tile retrieving, etc).

This would be particularly useful for work like gloss-osm, that allows immediate rendering by presenting missing tiles with a default until the download is complete.

[Thomas DuBuisson]

This is a patch that implements the proposal.

[Ben Lippmeier]

I've pushed this and exported the IO versions from their own modules. We should still change the event handling function of playIO to take an IO action, be consistent.

[Thomas DuBuisson]

Fix the event callback to be an IO action

[Thomas DuBuisson]

Replying to benl:

I've pushed this and exported the IO versions from their own modules. We should still change the event handling function of playIO to take an IO action, be consistent.

Done, see the new attachment.