add support for .env files

[amirreza8002]

closes#47

i have made these changes:

1- added django-environ as an optional dependency you could either make it a required dependency or make the methods more abstract so users can use whatever parsing tool they want.

2- add one optional parameter to use() and get_settings_instance() methods if the user provides a path, it will be used othersie it defaluts to None and methods go as they did before if a file path is given but the file doesn't exist, fallback to os.environ. (useful for ci/cd when .env file isn't available) also some safty check just in case, and some docstrings

3- added .idea to .gitignore for pycharm

let me know if you have any thoughts on this