Allow to use multiple-characters delimiter to separate column: withColumnSeparator

(from https://github.com/FasterXML/jackson-dataformat-csv/issues/141 by @jefferyyuan)

It's common that we use multiple-characters delimiter to separate columns in CVS: such as: [|]
Sometimes, we have no choice as third-party defines the csv format like that.

Sample data:

```
FirstName[|]LastName[|]Address
John[|]Smith[|]123 Main St.
```

https://github.com/FasterXML/jackson-dataformat-csv/issues/92 supports to use multiple characters as array element separator, It would be great if same can be done for withColumnSeparator.

I did some google search: seems there is no java library that supports use multiple-characters as the column separator.

But the C# CsvHelper does
https://github.com/JoshClose/CsvHelper