load method
Parses environment variables in filenames
and adds them to the underlying Map.
Logs to stderr if any file does not exist.
Implementation
void load(
[Iterable<String> filenames = const ['.env'],
Parser psr = const Parser()]) {
for (var filename in filenames) {
var f = File.fromUri(Uri.file(filename));
var lines = _verify(f);
_map.addAll(psr.parse(lines));
}
}