Adding Marked 2 plugin

plugins/marked/marked.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
+}