Add global method resolve(fileName)

lib/api/encodeGlobal.js

@@ -1,3 +1,4 @@
+var path = require('path');
 var Promise = require('../utils/promise');
 var PathUtils = require('../utils/path');
 var fs = require('../utils/fs');
@@ -67,6 +68,16 @@ function encodeGlobal(output) {
             return bookFS.readAsString(fileName);
         },
 
+        /**
+            Resolve a file from the book root
+
+            @param {String} fileName
+            @return {String}
+        */
+        resolve: function(fileName) {
+            return path.resolve(book.getContentRoot(), fileName);
+        },
+
         template: {
             /**
                 Apply a templating block and returns its result