Duckduckgo-search

1) update USERAGENTS,
2) def _text_api(): update payload,
3) update README.md

1. CLI: download_file - bugfix exceptions,
2. CLI: download_file() - change timeout=10,
3. CLI: _download_results() - change default threads=10,
4. CLI - add proxy parameter to news, videos, answers, suggestions, maps, translate.

1. bugfix in DDGS.text(backend='lite'): removed duplicated results
2. CLI: add `proxy` and `threads` parameters to `ddgs text` and `ddgs images`

1. del sleep() in text(backend='api') and images()
2. CLI: add aiofiles to save files asynchronously
3. _text_api() - del repeated self._normalize(body)
4. _normalize_url(): return '' if not url
5. CLI: small formatting changes
6. update type hints

1) normalize urls (unquote and replace spaces with +),
2) CLI: bugfix in maps() 'source' printing (was splitted),
3) CLI: download files asynchronously.

1) update USERAGENTS (only the most popular ones are left),
2) take a random user-agent when initializing DDGS,
3) bug fix in text(backend="api") - body was not normalized ,
4) bug fix in text(backend="lite") - url was not added to cache to check uniqueness of results,
5) update README.