Freeze PREFIX_KEY and PREFIX_VALUE of FixedLayout
Remove unused constant FixedLayout::ItemrefMixin::RENDITION_LAYOUT_PREFIX
Use __send__ instead of module_eval
Add Item#itemref
Add methods around rendition to ItemMixin
Make Manifest#<< return self
Make Spine#<< return self
Add ContentDocument::XHTML#top_level?
Implement FixedLayout::ContentDocumentMixin
Add note about timing of call for Rendition#def_rendition_methods
Define Spine::Itemref#page_spread and #page_spread=
Fix a typo
Redefine Itemref#page_spread and #page_spread= in FixedLayout module
Define Itemref#item=
Update changelog
Move files for wiki to docs directory
Fix links in docs
Include FixedLayout on parsing
Add comment for PackageMixin#using_fixed_layout