Duckduckgo-search

1. the code is rewritten as a class to make it easier to use with a proxy.
2. the VQD_CACHE is deleted pending clarification because vqd's for some reason changes.
3. ddg, ddg_images, ddg_videos, ddg_news, ddg_answers, ddg_suggestions, ddg_translate, ddg_maps functions are now deprecated. They will be removed in the future.
4. output and download parameters were removed from the functions and the functionality was moved to the CLI module.
5. issue templates added.

Remove '=' from f-strings for python 3.7 compatibility

1. BUGFIX in _get_vqd(). Replace `'` by `"` https://github.com/deedy5/duckduckgo_search/commit/56908f82c7ea5b079ade64842c59f60339afef5e
2. improve logging

refresh_vqd if '506.js' in resp.url

1. don't close VQD_CACHE after each access operation

store the cache in the module directory by default