- `set_key` and `unset_key` only modified the affected file instead of
parsing and re-writing file, this causes comments and other file
entact as it is.
- Add support for `export` prefix in the line.
- Internal refractoring ([theskumar])
- Allow `load_dotenv` and `dotenv_values` to work with `StringIO())` ([alanjds])([theskumar])([78])