build(aio): implement the remark renderer

The implementation adds three plugins to the remark processor:

* remove support for code blocks triggered by indented
text - only gfm triple backticks are supported; and also adds support for
dgeni inline tags.

* ignore content within `code-example` and `code-tabs` elements. This prevents
the content being accidentally treated as markdown

* ignore dgeni inline tags, e.g. `{@link ... }` to prevent the content of
the links from being accidentally treated as markdown

aio/transforms/remark-package/index.js

@@ -0,0 +1,9 @@
+var Package = require('dgeni').Package;
+
+/**
+ * @dgPackage remark
+ * @description Overrides the renderMarkdown service with an implementation based on remark
+ */
+module.exports = new Package('remark', ['nunjucks'])
+
+                     .factory(require('./services/renderMarkdown'));