Update to 3.0.0

- Add fromJson factories for all objects
- Make some properties use getters, to reduce redundant data
- Make all objects comparable with the equatable package
- Make all objects immutable with a constant constructor
    as a result of making them comparable

lib/api.dart

@@ -53,10 +53,7 @@ Future<PhrasePageScrapeResult> scrapeForPhrase(String phrase) async {
   final uri = uriForPhraseScrape(phrase);
   final response = await http.get(uri);
   if (response.statusCode == 404) {
-    return PhrasePageScrapeResult(
-      query: phrase,
-      found: false,
-    );
+    return PhrasePageScrapeResult(query: phrase);
   }
   return parsePhrasePageData(response.body, phrase);
 }