Implemented mouse and keyboard events
 - zoom with the middle mouse button
 - move entities with the right mouse button
 - change perspective with 'o' and 'p' respectively

The camera saves the viewport ratio
Added trace mode for the logger
added very simple polyhedron for manual testing
added visual indent to logging
implemented smoothing of surface normals
Implemented reshaping
 - the camera maintains ratio, aspect ratio and a ratio reference
 - changes on the viewport are correctly translated to the scene
implemented util.Color
removed obsolete color property
implemented render.Light and render.Material