Issue#8

1. Refactored Chunk to use the unity "Bounds" object instead of weird system of storing things in vector2s
2. There's also an inline comment in Chunk you should check out about how positions are generated
3. Refactored some of ChunkManager, mostly just to being it inline with the new bounds system. It's a big mess of complicated code in there so I could probably do some better reviewing with more comments explaining what stuff is meant to do.

I see one general problem with this generation technique. When you place an object it could obviously hang over the edge of a chunk into the next chunk - if you go with my suggestion of preventing overlaps (see inline comment in Chunk.cs) that's going to fail at chunk boundaries. I'm not sure how best to resolve this, it's a weakness of a chunk based system really.

Signed-off-by: Martin Evans <martindevans@gmail.com>