addMacro method
Implementation
void addMacro(String name, String content) {
// TODO(srawlins): We have to add HTML fragments after documentation is
// built, in order to include fragments which come from macros which
// were generated by a tool. I think the macro/HTML-injection system needs
// to be overhauled to allow for this type of looping.
//assert(!_localDocumentationBuilt);
_macros[name] = content;
}