Interactivity

this branch adds some methods to get data from the torque raster though the method getValueForPos. It allows to do interactive maps as shown in leaflet_interaction.html example.

Also I've updated the documentation (it was a bit outdated) and added the new methods
the thing here is that it does not matter so much, this if discards points outside the tile but the actual check is done inside the renderer function. I will change (also I will use Constants)