Create a new axis for "in refunds" on the sales by date report. Include
the refunds in the included time period. Refunds do not reduce the sales
total in the report.
* fixed indentation - swapped spaces for tabs at start of line, swapped
tabs for spaces min-line for alignment
* removed instances of `@return void` and `@access public`
* improved readability
@see http://make.wordpress.org/core/handbook/coding-standards/php/
Chuck Mac
Nicola Mustone
Mike Jolley
Tamara Zuk
Coen Jacobs