clear method
void
clear()
Implementation
void clear() {
svg = SVGDocument(addHeader:true,edgeOnly: true);
svg.setAttribute('viewBox','${-widthHalf} ${-heightHalf} $width $height');
svg.setAttribute('width', width.toString());
svg.setAttribute('height', height.toString());
_pathCount = 0;
_currentPath = '';
_currentStyle = '';
svg.style['background-color'] = _clearColor.getStyle();
}