Add base for plugin JS api

lib/api/encodeConfig.js

@@ -0,0 +1,30 @@
+var objectPath = require('object-path');
+var deprecate = require('./deprecate');
+
+/**
+    Encode a config object into a JS config api
+
+    @param {Output} output
+    @param {Config} config
+    @return {Object}
+*/
+function encodeConfig(output, config) {
+    var result = {
+        values: config.getValues().toJS(),
+
+        get: function(key, defaultValue) {
+            return objectPath.get(result.values, key, defaultValue);
+        },
+
+        set: function(key, value) {
+            return objectPath.set(result.values, key, value);
+        }
+    };
+
+    deprecate.field(output, 'config.options', result, 'options',
+        result.values, '"config.options" property is deprecated, use "config.get(key)" instead');
+
+    return result;
+}
+
+module.exports = encodeConfig;