markdown/pagemodel: Fixed regular expression to detect metadata

We only want to catch metadata keywords.
Other lines were caught with the former regular expression such
as heading containing a colon.

plugin/src/winterwell/markdown/pagemodel/MarkdownPage.java

@@ -210,7 +210,7 @@ public enum KLineType {
 
 	private boolean multiMarkdownSupport = true;
 	// TODO meta-data, footnotes, tables, link & image attributes
-	private static Pattern multiMarkdownTag = Pattern.compile("(.+):(.*)");
+	private static Pattern multiMarkdownTag = Pattern.compile("^([\\w].*):(.*)");
 	private Map<String, String> multiMarkdownTags = new HashMap<String, String>();
 
 	// Regular expression for Github support