Haskell based invoices

The following tools are used:

• clay library to generate CSS
• lucid library to generate HTML
• wkhtmltopdf to generate a PDF from HTML

To generate the first invoice, run

$ stack build && stack exec invoice -- oct-2016 | wkhtmltopdf - oct-2016.pdf

The invoice executable will generate the HTML invoice. wkhtmltopdf reads it from stdin and transforms it into a PDF. You can find an example generated file here.