Option for addBuffer to compress if smaller?

[AlexanderOMara]

It would be nice to have an option to have addBuffer compress the buffer if that makes the resulting file smaller.

I'm not sure it would really work for addFile but it would for addBuffer because the entire buffer is available at once.

I can make the pull request if the API can be decided on. Maybe one of the following?

addBuffer(buffer, path, {
    compress: null
});

addBuffer(buffer, path, {
    compress: 'auto'
});

addBuffer(buffer, path, {
    compress: 'smaller'
});