Part of #5: NPC moves, and collides with solid objects.
Part of #5: NPC has animation, stops on collision, resumes
Part of #5: Bounce when you hit an object.

- Fixed glitch with velocity being copied, not set
- Added helper to create walk cycle from this style of image
Resolved #5: NPC moves. Works very well with one-directional velocity.
Some refactoring; text follows the NPC.

- `Npc` is now `WalkingNpc`
- Velocity is set externally
- Talk is an NPC function
- Text follows the NPC, reappears.
Resolved #9: made second NPC type that walks around

Types are now `Npc` (slowly walks around) and `WalkingNpc` (fast walker)
Refactoring to meet Google style guidelines

http://google-styleguide.googlecode.com/svn/trunk/javascriptguide.xml