R1:f5c380bfc94c

Add very basic support for generating PDF documents

Summary: Ref T13358. This is very minimal, but technically works. The eventual goal is to generate PDF invoices to make my life easier when I have to interact with Enterprise Vendor Procurement.

Test Plan: {F6672439}

Maniphest Tasks: T13358

Differential Revision: https://secure.phabricator.com/D20692