dispose method

Implementation

void dispose(){
  if(_didDispose) return;
  _didDispose = true;

  emptyTextures.clear();
  equationToGL.clear();
  factorToGL.clear();
  buffers.clear();
  enabledCapabilities.clear();
  currentBoundFramebuffers.clear();
  defaultDrawbuffers.clear();
  currentBoundTextures.clear();

  extensions.dispose();
  currentDrawbuffers.dispose();
}