Move to SDK EInkDisplay and enable anti-aliased 2-bit text (#5)

* First pass at moving to SDK EInkDisplay library

* Add 2-bit grayscale text and anti-aliased rendering of text

* Render status bar for empty chapters

* Refresh screen every 15 pages to avoid ghosting

* Simplify boot and sleep screens

* Give FileSelectionScreen task more stack memory

* Move text around slightly on Boot and Sleep screens

* Re-use existing buffer and write to whole screen for 'partial update'

lib/Epub/Epub/Section.h

@@ -26,5 +26,5 @@ class Section {
   void setupCacheDir() const;
   void clearCache() const;
   bool persistPageDataToSD();
-  void renderPage() const;
+  Page* loadPageFromSD() const;
 };