Feature: go to text/start reference in epub guide section at first start (#156)

This parses the guide section in the content.opf for text/start
references and jumps to this on first open of the book.

Currently, this behavior will be repeated in case the reader manually
jumps to Chapter 0 and then re-opens the book. IMO, this is an
acceptable edge case (for which I couldn't see a good fix other than to
drag a "first open" boolean around).

---------

Co-authored-by: Sam Davis <sam@sjd.co>
Co-authored-by: Dave Allie <dave@daveallie.com>

lib/Epub/Epub/parsers/ContentOpfParser.h

@@ -15,6 +15,7 @@ class ContentOpfParser final : public Print {
     IN_BOOK_AUTHOR,
     IN_MANIFEST,
     IN_SPINE,
+    IN_GUIDE,
   };
 
   const std::string& cachePath;
@@ -35,6 +36,7 @@ class ContentOpfParser final : public Print {
   std::string author;
   std::string tocNcxPath;
   std::string coverItemHref;
+  std::string textReferenceHref;
 
   explicit ContentOpfParser(const std::string& cachePath, const std::string& baseContentPath, const size_t xmlSize,
                             BookMetadataCache* cache)