Newlines sourced as \\n string literals

```console
$ echo -e 'declare -x FOO="B\nA\nR\n"' > test
$ bass source ./test
$ echo "$FOO"
B\nA\nR\n
$ set -x FOO 'B
A
R
'
$ echo "$FOO"
B
A
R

$
```

compare bash:
```console
$ source ./test
$ echo "$FOO"
B
A
R

$
```