added line support;
added mini tutorial;
refactored the scene;
fixed remove child on group bug;
check if the child exists before removing it;
Updates the bounding box when the start and end point changes;
Label node added;
fixed convention;
label will be 1x1 until will find a great way to measure the width and height of the labels;
fixed the line when was a child and the parent absolute position was not (0, 0) the line would be in an invalid position;
fix: lines were very ugly because beginPath were not present;
fix: made it work cross-browser without errors;
fix: don't really know why setting the anchor changes the size of the node, therefore removed because was bugging in rectangle nodes;
added some tests for and anchor in a group;