Circle recognizer. The gesture can be made by one or more traces (starting and ending in a synchronized way, relatively to GROUPING_SYNCH_TIME). The algorythm will indistinctly recognize round paths covering the shape of a circonference (even passing more times on the same section). However the first and the last point of the path must be close to each other. A "bug" makes the GR to recognize as a circle also a 'C' if the path is closed enough (not much), and such that the extremes of the path are close to each other (you must draw the letter twice: forward and backward).