MarshalJSON outputs too many newlines

[bojanz]

Current implementation:

		// add key
		if err := encoder.Encode(k); err != nil {
			return nil, err
		}
		buf.WriteByte(':')
		// add value
		if err := encoder.Encode(o.values[k]); err != nil {
			return nil, err
		}

encoder.Encode will always add a newline:

	// Terminate each value with a newline.
	// This makes the output look a little nicer
	// when debugging, and some kind of space
	// is required if the encoded value was a number,
	// so that the reader knows there aren't more
	// digits coming.
	e.WriteByte('\n')

So we always get a newline after the key and after the value:

{"id"
:"123456"
,"status"
:"active"

This could be avoided by using json.Marshal(), but json.Marshal doesn't support turning off HTML encoding. So in order to preserve BC, we need to have a helper that will strip the last byte from the encoded output.