Minors updates on few .md files

* home.md : fix (features & colorspaces) links
* features.md : fix "Camera calibration with veejay" , "Reloaded", "TwinView / One BigDesktop", "Perspective Transform" links
* projector-camera-calibration-augmented-reality.md : fix result & start images & strong emphasis for keystrokes
* projection-mapping.md : emphasis light & strong