Book styling for images and captions

Resolves #12

Author: hollasch

style/book.css

@@ -27,3 +27,15 @@ div.warning p.title {
     font-weight: bold;
     color:       red;
 }
+
+/* Images and Figures */
+
+.md img {
+    margin-top: 1.5em;
+    width: 72ex;
+}
+
+.md div.imagecaption {
+    text-align: center;
+    margin-bottom: 1em;
+}