DAISY 2.02 Validator

This is a port of the "Daisy 2.02 DTB Light Validator" included in Pipeline 1. This implementation does not yet support validation of the MP3 files themself.

I've developed this on the same branch as the EPUB3 to DAISY 2.02 script, which is why the commit log contains some of those commits. However, this PR only contains the DAISY 2.02 Validator script and can be merged independently. The EPUB3 to DAISY 2.02 script will be in a separate PR.

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I haven't really tested but full-text books might cause a problem I suppose.

The biggest DTBook we have is 7 MB (Biology textbook). Our "TV-Guide" DAISY 2.02 has 1 content HTML file at 4,7MB and 150 SMIL files at a total of 6MB (this production used to include a lot more files, 5000 or something I think, but now we're not creating separate SMILs for the deepest levels anymore I think).

How big do you think the Worlds Biggest DAISY 2.02 Production is?

I found this to be the easiest solution. The alternative I can think of is to first build a XML document listing all possible references by iterating over all the documents; then passing that document to a XSLT similar to the one used. I'm not sure if it would be more efficient or not as Calabash would perform a lot more of the job; Saxon is much more efficient at these things in my experience. The issue would be if the combined document is too big to be represented in memory maybe.

Do you have any ideas for a pattern that might be more efficient?