Fix og:image to an absolute shared URL; add og-image.jpg at the root

og:image was relative (img/og_image.jpg) which scrapers can't resolve. Point it at the
shared https://davidwindham.com/og-image.jpg and ship the image at the web root.

index.html

@@ -15,7 +15,7 @@
 <link rel="canonical" href="https://davidwindham.com/">
 <meta property="og:title" content="David Windham">
 <meta property="og:description" content="Something Else">
-<meta property="og:type" content="website"><meta property="og:url" content="https://davidwindham.com"><meta property="og:site_name" content="David Windham"><meta property="og:image" content="img/og_image.jpg"><meta property="fb:app_id" content="203136806559589"><meta name="twitter:site" content="@windhamdavid"><meta name="twitter:creator" content="@windhamdavid"><meta name="twitter:title" content="David Windham"><meta name="twitter:description" content="Something Else"><meta name="twitter:image" content="img/ogt_image.jpg"><meta name="twitter:card" content="summary_large_image"><link rel="apple-touch-icon" sizes="180x180" href="img/icons/apple-touch-icon.png"><link rel="icon" type="image/png" sizes="32x32" href="img/icons/favicon-32x32.png"><link rel="icon" type="image/png" sizes="16x16" href="img/icons/favicon-16x16.png"><link rel="manifest" href="img/icons/site.webmanifest"><!--<link rel="mask-icon" href="img/icons/safari-pinned-tab.svg" color="#3f3f3f">--><meta name="msapplication-TileColor" content="#000000"><meta name="theme-color" content="#ffffff">
+<meta property="og:type" content="website"><meta property="og:url" content="https://davidwindham.com"><meta property="og:site_name" content="David Windham"><meta property="og:image" content="https://davidwindham.com/og-image.jpg"><meta property="fb:app_id" content="203136806559589"><meta name="twitter:site" content="@windhamdavid"><meta name="twitter:creator" content="@windhamdavid"><meta name="twitter:title" content="David Windham"><meta name="twitter:description" content="Something Else"><meta name="twitter:image" content="img/ogt_image.jpg"><meta name="twitter:card" content="summary_large_image"><link rel="apple-touch-icon" sizes="180x180" href="img/icons/apple-touch-icon.png"><link rel="icon" type="image/png" sizes="32x32" href="img/icons/favicon-32x32.png"><link rel="icon" type="image/png" sizes="16x16" href="img/icons/favicon-16x16.png"><link rel="manifest" href="img/icons/site.webmanifest"><!--<link rel="mask-icon" href="img/icons/safari-pinned-tab.svg" color="#3f3f3f">--><meta name="msapplication-TileColor" content="#000000"><meta name="theme-color" content="#ffffff">
 <!-- build:css css/dw.css -->
 <link rel="stylesheet" href="css/fullcalendar.css">
 <link rel="stylesheet" href="css/styles.css">