Support for archive formats PDF/A-1 and A-3

[26labs]

These formats are important to business use particularly the A3 which is a signed PDF with embedded XML data. Will become mandatory in EU, starting with Germany. This could take this library from being a fine achievement to being a necessity for Goloang developers in enterprises and by inference a great way to prompt developers of other languages to move to Go (guerilla marketing some would call it).

[jung-kurt]

Thanks for the comments and confidence in the project, @26labs. I was not even aware of the PDF/A archival standard. The big task will be to support digital signing (see issue 115); beyond that, it looks like it is a matter of assuring that certain features like transparency, linked fonts, etc are not used.

[THausherr]

It is not THAT difficult for simple documents: always embed fonts (don't use the standard 14), have an XMP metadata stream, and an outputintent. Here's a very simple PDF/a-1b file. PDFA.pdf