Added current drafts

 - sigma.plugins.neighborhoods
 - some other examples
sigma.webgl.edges.arrow works

The edge renderer sigma.webgl.edges.arrow is now implemented. It is way more expensive than the default renderer, especially due to the fact that, with the current architecture, every points of the arrows have to be generated through the same vertex shader, which makes it pretty heavy.
Fixed #161: Multi-touch wrong positions

Had to add the sigma.utils.getOffset function that recursively retrieves the global offset of a DOM element. With this function and the pageX / pageY of the Touch objects, the positions of the points are now good, and the multiu-touch is now fully working.
Added sed Grunt task, to manage examples imports

This task just takes the array of every core JS files, makes an array of HTML <script> tags, and replaces the list of dependencies in every example files. The goal is just to not have to write in every examples when a new source file is added.
Cleaning examples with sed for arrows
sigma.canvas.edges.arrow works

The canvas arrow renderer is now fully implemented.