Add StackOverflow username validator

user_scanner/community/__init__.py

@@ -0,0 +1 @@
+# community

user_scanner/community/stackoverflow.py

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+from user_scanner.core.orchestrator import generic_validate
+from user_scanner.core.result import Result
+
+def validate_stackoverflow(user: str) -> Result:
+    url = f"https://stackoverflow.com/users/filter?search={user}"
+
+    def process(response):
+        if response.status_code == 200:
+            text = response.text
+
+            if "No users matched your search." in text:
+                return Result.available()
+
+            pattern = f'>{user}<'
+            if pattern in text:
+                return Result.taken()
+
+            return Result.available()
+
+        return Result.error("Unexpected status code from Stack Overflow")
+
+    return generic_validate(url, process)
+
+
+if __name__ == "__main__":
+    user = input("Username?: ").strip()
+    result = validate_stackoverflow(user)
+
+    if result == Result.available():
+        print("Available!")
+    elif result == Result.taken():
+        print("Unavailable!")
+    else:
+        msg = result.get_reason()
+        print("Error occurred!" + msg)