feat(aio): code snippet source available & shown when code missing

Tells reader (usually the author) what code file is missing
Also when no linenums specified, turn them on if num of lines > 10

aio/tools/transforms/examples-package/processors/render-examples.js

@@ -17,8 +17,6 @@ module.exports = function renderExamples(getExampleRegion) {
             if (attrMap.path) {
               // We found a path attribute so look up the example and rebuild the HTML
               const exampleContent = getExampleRegion(doc, attrMap.path, attrMap.region);
-              delete attrMap.path;
-              delete attrMap.region;
               attributes = Object.keys(attrMap).map(key => ` ${key}="${attrMap[key].replace(/"/g, '"')}"`).join('');
               return `<${element}${attributes}>\n${exampleContent}\n</${element}>`;
             }