dotenv extension does not support multiline values

Usually .env files are allowed to contain new lines if the value is surrounded by double quotes. The simple line splitting that dotenv does not support that case.

Minimal reproduction case:
`.env`
```
TEST="some
text"
```
Result is an error `Error in fail: Invalid format for dotenv file: ...`, while the file should be parsed correctly and put `TEST="some\ntext"` in the environment.