Merge pull request #3060 from chrisfsmith/feature/marked

Adding Marked 2 plugin (OS X only)

plugins/marked2/README.md

+## marked2
+
+Plugin for Marked 2, a previewer for Markdown files on Mac OS X 
+
+### Requirements
+
+ * [Marked 2](http://marked2app.com)
+
+### Usage
+
+ * If `marked` is called without an argument, open Marked
+
+ * If `marked` is passed a file, open it in Marked

plugins/marked2/marked2.plugin.zsh

+#
+# If marked is called without an argument, open Marked
+# If marked is passed a file, open it in Marked
+#
+function marked() {
+    if [ "$1" ]
+    then
+        open -a "marked 2.app" "$1"
+    else
+        open -a "marked 2.app"
+    fi
+}