added silver_price_chart_init

git-svn-id: https://plugins.svn.wordpress.org/gold-price-chart-widget/trunk@973587 b8457f37-d9ea-0310-8a92-e5e31aec5664
update changelog

git-svn-id: https://plugins.svn.wordpress.org/gold-price-chart-widget/trunk@973589 b8457f37-d9ea-0310-8a92-e5e31aec5664
update stable

git-svn-id: https://plugins.svn.wordpress.org/gold-price-chart-widget/trunk@973590 b8457f37-d9ea-0310-8a92-e5e31aec5664