unfold method
Implementation
String unfold(String s) => s
// https://tools.ietf.org/html/rfc2425#section-5.8.1
.replaceAll(RegExp(r'\n[ \t]'), '')
// Quoted-encoded contents are sometimes split on multiple lines ending and
// starting with '='.
.replaceAll(RegExp(r'=\n='), '=');