Issue #99 : withTouch() touchstart event was relying on direct access to...

Issue #99 : the withTouch() touchstart event handler was relying on direct access to the Processing.eventHandlers array to remove any existing mouse event handlers.

Instead of exposing Processing.eventHandlers array directly, this change exposes a method called detachEventHandlersByTypeMatch() which takes a regex of event types, iterates through the list of existing event handlers, and detaches the handlers that match.

The withTouch() touchstart handler then calls detachEventHandlersByTypeMatch() with a regex that matches the desired mouse events.
Yes, I'll fix the indenting.

I didn't use `array.forEach` because it isn't supported on all browsers, but since ProcessingJS requires HTML5, that's not an issue here :)

However, I want to avoid having to pass `eventHandlers` into `detachEventHandlersByType`, because `eventHandlers` being out of scope of the caller is the whole reason for this bug.

I'll update my pull request.