Consider allowing direct POI calls when Loiste doesn't support something

[Deraen]

• Cells
  • Extend clj map write to support callback taking Cell object?
• Rows
  • Extend clj map write to support callback taking the Row object? Before or after the cells are written?
• Styles
  • Extend write-rows! :styles option to take a callback fn taking the CellStyle object.
• Columns
  • Columns don't really exist, it is just Loiste abstraction over a few Sheet properties.
• Sheet
  • OK. sheet return value.
• Workbook
  • OK. workboot or streaming-workbook return value.
• Styles
  • font add callback
  • border, fill-pattern allow enum values directly