0.4.0

• BREAKING CHANGE: Add option to choose between comma and tab as delimiter
  • Default delimiter changed to tab ('\t'), which creates TSV files
  • File extension now depends on delimiter: .csv for comma, .tsv for tab
  • MIME type now depends on delimiter: text/csv for comma, text/tab-separated-values for tab
  • All API methods now accept a delimiter parameter
  • download API now accepts an options object with delimiter property
  • Default filename extension changed from .csv to .tsv when using default delimiter
• Add support for XLSX format output
  • New toXlsx method to convert data to XLSX workbook
  • Add format option to toBlob, toHref, and download methods
  • Auto-detect XLSX availability with fallback to CSV/TSV
  • Set appropriate MIME type and file extension based on format
  • Add dependency on SheetJS library (xlsx.js)