Fix #1665

[jonsequitur]

This removes the distinction between line-delimited and space-delimited response files, fixing #1665.

It does this by generalizing the mechanism where tokens prefixed with @ can be replaced with other tokens. Response files are one example of this but now alternative mechanisms can be introduced.

var parser = new CommandLineBuilder(command)
             .UseTokenReplacer((string tokenToReplace, out IReadOnlyList<string> tokens, out string message) =>
             {
                 tokens = new[] { "123" };
                 message = null;
                 return true;
             })
             .Build();

var result = parser.Parse("@interpolate-me");

result.GetValueForArgument(argument).Should().Be(123);

[Keboo]

Should this test also assert on the value of tokenToReplace? I assume in this situation it would be "@interpolate-me" or would it be "interpolate-me"?

[jonsequitur]

I'll add a test for this. The received tokenToReplace will not include the @. Open to changing that. My assumption was that this should be transparently removed, sort of like quotation marks.

[Keboo]

That sounds good to me