Add method to update multiple key/values to .env

[mrjng]

update_dict_to_dotenv was implemented to support for updating multiple environment variables at once. This method is necessary because set_key can update only one environment variable at once.

Feel free to ask any questions or give your opinion. Thanks.

Following things were changed.

• update_dict_to_dotenv was added to main.py
• make_env_line was extracted from set_key
• test_update_dict_to_dotenv was added to test_main.py
• Update tests/__init__.py to import update_dict_to_dotenv

[mrjng]

@theskumar Could you take a look at this PR?

[mrjng]

I make the commit history clearer.