pdfsig: Add support for specifying signature by field name
Currently pdfsig
uses the numerical order of the signature field in the document (1,2,3,...) based on the way the signature fields are present in the PDF. This ordering can change based on the way the document is generated (plus it can be tedious to find the correct signature when there are a number of them). This patch adds support for finding the signature based on the field name in the document.