Allow setting delimiter as a part of the constructor

[yashshah1]

https://github.com/mbrn/filefy/blob/fd154dbb84ebe3b93f97726d644d3e5f151cbca8/src/csv-builder/CsvBuilder.ts#L10

A default value of , can be set if required. Something like:

constrcutor(fileName: string, delimiter: strinng = ",") {