Render entities

[bentref]

We have to render the following entities:

• Player (something better than a blue square)
• NPCs
• Objects (hazards, desirable items, etc)
• Perhaps some bitmap images to make things prettier/more detailed

To implement this as I like, need the ability to render tile occupants/entities as images on top of the tiles

[bentref]

Update: very basic player rendering (as a blue square) now works! I'm sure we can do better though so I'm not saying I'm done just yet :wink: