Remove redundant logging leftover from experimental phase of AMD/Require.js adoption.
Refactor smil_document_parser module.

* Use the parser object for storing publication-wide state.
* Stop storing ephemeral media-overlay item level state in the parser object.
* Make the module into a proper parser prototype.
* Stop the module from instantiating its own instances.
Merge pull request #36 from readium/feature/epub-module-refactoring

Feature/epub module refactoring