Fixed handling of SVG Content Documents.
 - _$epubHtml is loaded with <svg> element if no <html> element is found.
 - _meta_size is loaded from <svg> element's width & height attributes if necessary.
Merge branch 'develop' of https://github.com/readium/readium-shared-js into develop

* 'develop' of https://github.com/readium/readium-shared-js:
  Bugfix-33 Allow elements to have a period in IDs.