Support multiline values

[gonzaloriestra]

Adds support for multiline values:

echo -e "a=\"1\n2\"\nb=3" | npm run our:bin env2json
  {"a":"1\n2","b":"3"}

echo '{"a":"1\\n2","b":3}' | npm run our:bin json2env
  a="1\n2"
  b=3

[gonzaloriestra]

@balupton could you please review this? Thanks!

[balupton]

Tests failed on Windows. Can you fix or reproduce that locally?

[balupton]

Actually seems the windows failure is prior to this PR
https://github.com/bevry/envfile/actions/runs/7360505711

will merge so it gets published to the @next npm tag, and then will look into windows and publishing to latest either this week or next week

if you can fix the windows tests, in a subsequent PR that would be awesome!

[balupton]

Actually, leave the windows issue with me. I believe I know what it is.