Draw active hotbar item indicator on top
Updates manpages

Fixes #27
Misc. fixes

- Some big changes in the terrain generation, more to come
- F3 for debug info
- Lua support for entity bounding boxes
- Fixed a few concurrency problems
- Sketch of a flex/bison parser for configuring the terrain
  generators with actual expressions
- Fixes #24
- Fixes #27
- Fixes #29