add option for a max buffer size

Add an option to set a max buffer size that will send an `error` event if `byline` has buffered a more than `maxBuffer` and still hasn't seen a `newline`
I don't think this testing should be performed with an external file. If your logic is correct, the test should be sufficient with a max buffer size of 10 characters. Is there some way you can provide a test object that has the same interface as that returned by fs.createReadStream(), but which returns a line of 11 characters?

Tests which rely on external files, while they work, can be painful to debug.