The build.xml file has been moved to /frameworks/cocos2d-html5/tools/build.xml.
A node.js script tool has been added in v3.0a, it also in directory /frameworks/cocos2d-html5/tools/publish.js.
Please copy tools to your project directory and config your project.json, then run the tools/publish.js in node.js, it will be compile your proejct.
And if you create a new project by cocos2d-console command "cocos new aGameProject -l js".
You can publish your CH5 game by this command:
"cocos run -p web -m release"
Hopes to help