Add some more style information.

doc/reference.html

@@ -85,6 +85,9 @@ div.contents ul.contents {
 }
 .variable {
 }
+h1, h2, h3, h4, h5, h6 {
+  page-break-inside: avoid;
+}
 blockquote {
   border: solid thin gray;
   box-shadow: 3px 3px 5px rgba(0,0,0,0.5);

mxmldoc.c

@@ -5422,6 +5422,9 @@ write_html_head(FILE       *out,	/* I - Output file */
 	  "}\n"
 	  ".variable {\n"
 	  "}\n"
+	  "h1, h2, h3, h4, h5, h6 {\n"
+	  "  page-break-inside: avoid;\n"
+	  "}\n"
 	  "blockquote {\n"
 	  "  border: solid thin gray;\n"
 	  "  box-shadow: 3px 3px 5px rgba(0,0,0,0.5);\n"