add method
Adds a DartdocOption to the children of this DartdocOption.
Implementation
void add(DartdocOption option) {
if (_children.containsKey(option.name)) {
throw DartdocOptionError(
'Tried to add two children with the same name: ${option.name}');
}
_children[option.name] = option;
// TODO(jcollins-g): Consider a stronger refactor that doesn't rely on
// post-construction setup for [parent].
option.parent = this;
}