Added basic SourceForge support

lib/app_sources/sourceforge.dart

@@ -0,0 +1,69 @@
+import 'package:html/parser.dart';
+import 'package:http/http.dart';
+import 'package:obtainium/app_sources/github.dart';
+import 'package:obtainium/components/generated_form.dart';
+import 'package:obtainium/providers/source_provider.dart';
+
+class SourceForge implements AppSource {
+  @override
+  late String host = 'sourceforge.net';
+
+  @override
+  String standardizeURL(String url) {
+    RegExp standardUrlRegEx = RegExp('^https?://$host/projects/[^/]+');
+    RegExpMatch? match = standardUrlRegEx.firstMatch(url.toLowerCase());
+    if (match == null) {
+      throw notValidURL(runtimeType.toString());
+    }
+    return url.substring(0, match.end);
+  }
+
+  @override
+  Future<APKDetails> getLatestAPKDetails(
+      String standardUrl, List<String> additionalData) async {
+    Response res = await get(Uri.parse('$standardUrl/rss?path=/'));
+    if (res.statusCode == 200) {
+      var parsedHtml = parse(res.body);
+      var allDownloadLinks =
+          parsedHtml.querySelectorAll('guid').map((e) => e.innerHtml).toList();
+      getVersion(String url) {
+        try {
+          var tokens = url.split('/');
+          return tokens[tokens.length - 3];
+        } catch (e) {
+          return null;
+        }
+      }
+
+      String? version = getVersion(allDownloadLinks[0]);
+      if (version == null) {
+        throw couldNotFindLatestVersion;
+      }
+      var apkUrlListAllReleases = allDownloadLinks
+          .where((element) => element.toLowerCase().endsWith('.apk/download'))
+          .toList();
+      var apkUrlList =
+          apkUrlListAllReleases // This can be used skipped for fallback support later
+              .where((element) => getVersion(element) == version)
+              .toList();
+      if (apkUrlList.isEmpty) {
+        throw noAPKFound;
+      }
+      return APKDetails(version, apkUrlList);
+    } else {
+      throw couldNotFindReleases;
+    }
+  }
+
+  @override
+  AppNames getAppNames(String standardUrl) {
+    return AppNames(runtimeType.toString(),
+        standardUrl.substring(standardUrl.lastIndexOf('/') + 1));
+  }
+
+  @override
+  List<List<GeneratedFormItem>> additionalDataFormItems = [];
+
+  @override
+  List<String> additionalDataDefaults = [];
+}