Further fixes to CSS URL regexps

This commit brings the CSS url() and @import parsing logic closer to the
conditional branching parsing logic dictated by the CSS specification.
Remove a TODO comment that has been addressed by the previous commit
Merge pull request #44 from readium/hotfix/css-url-regexps

Hotfix/css url regexps
fixed InDesign obfuscated font + video sample book rendering (base href XHTML in head, not body!)
Merge branch 'develop' of github.com:readium/readium-js into develop
base-href at top of head, submodules
iframe contentDocument now reloaded using source attribute
Merge pull request #45 from readium/feature/iframeSourceFetch

programmatic asset fetch, iframe source attribute re-initialised (no contentDocument swap)
updtaed dependency
submodule
Fixing bug with heavy UI FXL books initially opened as single spread
[Bug 76] Fix. Introduced extera scaler div
submodule
Merge branch 'develop' into feature/chrome_ext_fonts