Goodbye HTML, hello XML

Replaced HTML exporting/parsing with XML exporting/parsing. Also
replaced the 'high-level' function call with 'low-level' pdfminer
usage.

The XML parser handled validation and suppression of header/footer
content on its own.

From the PDF parser, XML is dumped to a file. From the XML parser, CSV
is dumped to a file. The new timesheet parser should read in that CSV
file.