* Fix the build failure (Raymond Feng)

 * Fix the model-config/datasource merge (Raymond Feng)

 * Resolved style issue (Dennis Ashby)

 * Added code to allow model-config to respect model-config.local.js and model-config.env.js as do other config files. (Dennis Ashby)

 * Add jsdoc for `options.mixinSources` (Miroslav Bajtoš)

 * allow middleware to be optional (Hage Yaapa)