Merge branch 'develop' into feature/epub-module-refactoring
Move metadata and manifest parsing to package_document_parser
Elimination of endemic data structures for publication metadata.

This commit eliminates the storage of package metadata within JSON data
structures that are endemic to readium-js and uses a dedicated Metadata
object for that task instead.
Merge pull request #41 from readium/feature/epub-module-refactoring

Feature/epub module refactoring