Improve support of embedded CSV

[charphi]

The current implementation is inefficient because the internal buffer is recreated for each call.
There should be a way to reuse the buffer or the reader/writer between calls.

There is also a problem with the last end-of-line which is not welcome in some cases.

Embedded CSV example:

public class EmbeddedCSVDemo {

    public static void main(String[] args) throws IOException {

        Csv.Format embeddedFormat = Csv.Format.builder().delimiter('=').separator(",").build();

        StringWriter mainString = new StringWriter();
        try (Csv.Writer main = Csv.Writer.of(Csv.Format.DEFAULT, Csv.WriterOptions.DEFAULT, mainString)) {
            main.writeField("NAME");
            main.writeField("PROPERTIES");
            main.writeEndOfLine();

            for (Record record : Record.getData()) {
                main.writeField(record.getName());
                StringWriter embeddedString = new StringWriter();
                try (Csv.Writer embedded = Csv.Writer.of(embeddedFormat, Csv.WriterOptions.DEFAULT, embeddedString)) {
                    for (Map.Entry<String, String> property : record.getProperties().entrySet()) {
                        embedded.writeField(property.getKey());
                        embedded.writeField(property.getValue());
                        embedded.writeEndOfLine();
                    }
                }
                main.writeField(embeddedString.toString());
                main.writeEndOfLine();
            }
        }
        System.out.println(mainString);
    }

    @lombok.Value
    @lombok.Builder
    public static class Record {

        String name;

        @lombok.Singular
        Map<String, String> properties;

        static List<Record> getData() {
            List<Record> result = new ArrayList<>();
            result.add(Record.builder().name("name1").property("key1", "value1").build());
            result.add(Record.builder().name("name2").property("key2", "value2").build());
            return result;
        }
    }
}

Output:

NAME,PROPERTIES
name1,"key1=value1,"
name2,"key2=value2,"

[charphi]

Related work: osiegmar/FastCSV#63