Finalize TouchEvent class

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https://github.com/processing/processing-android/blob/master/core/src/processing/event/TouchEvent.java

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This should take care of issues such as #256, #246, and #245

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fd3098c

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Working on multitouch (and other Android-specific) API in this branch https://github.com/processing/processing-android/tree/multitouch. Will merge back into master once discussed and agreed upon: #273

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Some notes about the current implementation:

• Based on how Android handles basic touch events, Processing generates three touch events: start, move, and end.
• The start event is triggered when any (primary or non-primary) touch pointer goes down.
• The move event is triggered when a touch pointer changes position.
• The end event is triggered when a touch pointer goes up.
• Following p5.js touch API, PApplet has a touches array of TouchEvent.Pointer elements, containing unique pointer ID, X/Y coordinates, as well as size and pressure, as returned by MotionEvent.getSize() and MotionEvent.getPressure().
• The callback methods for these events are touchStarted(), touchMoved(), and touchEnded().

Example of use:

void setup() {
  fullScreen();
  noStroke();
}

void draw() {
  background(255);
  for (int i = 0; i < touches.length; i++) {
    ellipse(touches[i].x, touches[i].y, 100, 100);
  }
}

void touchStarted() {
  println("Touch started");
}

void touchEnded() {
  println("Touch ended");
}

void touchMoved() {
  println("Touch moved");
}

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Some observations concerning the touch events:

• When the start/move/end event occur, there is no way to determine which entries in the touches array are being involved in the event, unless one keeps compares the current contents of touches with a previous copy

• Start/end events are associated with a single pointer (but the touch array might contain several elements, since some pointers might be down when a new one is detected or released)

• A single move event could involve several pointers (while some other pointers remain unchanged)

So, is there the need for an additional variable, say pointers, which contains the IDs (or indices) of only the pointers involved in the current event? This variable would be needed to access only the elements in the touches array that correspond to such pointers.

Another group of observations concern the previous values of the touch points:

• Should the previous X and Y coordinates being saved in some other set if variables, analogous to pmouseX/pmouseY?

• What about pressure/size values?

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Finalized with 75362fe and b72887d