Consolidate chapter page data into single file (#144)

## Summary

* Consolidate chapter page data into single file
* Header structure of the file stays the same, following the page count,
we now put a LUT offset
   * The page data is all then appended to this file
* Finally the LUT is appended to the end of the file, and the page count
is updated
* This will also significantly improve the duration of cache cleanup
which takes a while to scan the directory and cleanup content
* Remove page file version as it's all tied up into the section file now
* Bumped section file version to 7
* Moved section content into sub directory
* Updated docs

## Additional Context

* Benchmarks:
  * Generating 74 pages of content from a chapter in Jade Legacy took:
    * master: 6,229ms
    * this PR: 1,305ms
    * Speedup of 79%
  * Generating 207 pages of content from Livesuit book:
    * With progress bar UI updates:
      * master: 24,250ms
      * this PR: 8,063ms
      * Speedup of 67%
    * Without progress bar UI updates:
      * master: 13,055ms
      * this PR: 3,600ms
      * Speedup of 72%

lib/Epub/Epub/blocks/TextBlock.cpp

@@ -24,34 +24,33 @@ void TextBlock::render(const GfxRenderer& renderer, const int fontId, const int
   }
 }
 
-void TextBlock::serialize(File& file) const {
-  // words
-  const uint32_t wc = words.size();
-  serialization::writePod(file, wc);
+bool TextBlock::serialize(File& file) const {
+  if (words.size() != wordXpos.size() || words.size() != wordStyles.size()) {
+    Serial.printf("[%lu] [TXB] Serialization failed: size mismatch (words=%u, xpos=%u, styles=%u)\n", millis(),
+                  words.size(), wordXpos.size(), wordStyles.size());
+    return false;
+  }
+
+  // Word data
+  serialization::writePod(file, static_cast<uint32_t>(words.size()));
   for (const auto& w : words) serialization::writeString(file, w);
-
-  // wordXpos
-  const uint32_t xc = wordXpos.size();
-  serialization::writePod(file, xc);
   for (auto x : wordXpos) serialization::writePod(file, x);
-
-  // wordStyles
-  const uint32_t sc = wordStyles.size();
-  serialization::writePod(file, sc);
   for (auto s : wordStyles) serialization::writePod(file, s);
 
-  // style
+  // Block style
   serialization::writePod(file, style);
+
+  return true;
 }
 
 std::unique_ptr<TextBlock> TextBlock::deserialize(File& file) {
-  uint32_t wc, xc, sc;
+  uint32_t wc;
   std::list<std::string> words;
   std::list<uint16_t> wordXpos;
   std::list<EpdFontStyle> wordStyles;
   BLOCK_STYLE style;
 
-  // words
+  // Word count
   serialization::readPod(file, wc);
 
   // Sanity check: prevent allocation of unreasonably large lists (max 10000 words per block)
@@ -60,27 +59,15 @@ std::unique_ptr<TextBlock> TextBlock::deserialize(File& file) {
     return nullptr;
   }
 
+  // Word data
   words.resize(wc);
+  wordXpos.resize(wc);
+  wordStyles.resize(wc);
   for (auto& w : words) serialization::readString(file, w);
-
-  // wordXpos
-  serialization::readPod(file, xc);
-  wordXpos.resize(xc);
   for (auto& x : wordXpos) serialization::readPod(file, x);
-
-  // wordStyles
-  serialization::readPod(file, sc);
-  wordStyles.resize(sc);
   for (auto& s : wordStyles) serialization::readPod(file, s);
 
-  // Validate data consistency: all three lists must have the same size
-  if (wc != xc || wc != sc) {
-    Serial.printf("[%lu] [TXB] Deserialization failed: size mismatch (words=%u, xpos=%u, styles=%u)\n", millis(), wc,
-                  xc, sc);
-    return nullptr;
-  }
-
-  // style
+  // Block style
   serialization::readPod(file, style);
 
   return std::unique_ptr<TextBlock>(new TextBlock(std::move(words), std::move(wordXpos), std::move(wordStyles), style));