new module: io.{cpp,h}

Stub in interface for dumping depth map to file.
main.cpp: hack in dump support in frame-draw function
SceneDrawer.cpp: remove HACKS to dump to standard output
SceneDrawer.cpp: remove PrintJoint hack

The PrintJoint() function will not be needed soon.
io.cpp: add support for dumping joints
io.cpp: increase friendliness of log by naming joint fields
Merge pull request #7 from rjw57/io-playground

move logging to io.{cpp,h}