Demo menu

[ndouglas]

Story

There should be a menu, accessible from the main menu, that gates off demonstration technology, etc.

For instance, it'd be useful to show map generation, pathfinding, combat, etc demos.

Acceptance Criteria

• [x] A demo menu item has been created that permits access to demos.
• [x] The demo menu can be exited, whereupon the player should be presented with the main menu.

Implementation Notes

[ndouglas]