Fixes #61: Expose spine item linear property through JNI for Android.
Support for more rendition properties. Use proper fetching of page-spread property.
Merge pull request #128 from readium/feature/issue-61-spineitem-linear-android

Fixes #61, #131: Support for spine item linear and rendition:orientation/flow/spread properties.
Correct the createSpineItem signature for JNI.
adding "severity" information to the error handler, to suppress fatal exceptions when EPUB Critical/Major error is encountered during SDK parsing. See https://github.com/readium/SDKLauncher-iOS/issues/45
addresses https://github.com/readium/SDKLauncher-Android/issues/33 (removed fatal exception when opening incorrect EPUBs (e.g. EPUB2 with missing metadata) by introducing a proper error handler)
quickfix (follow-up to previous commit): free JNI-allocated string
sorry, the Java file was not automatically added by the IDE in my previous commit
Merge branch 'develop' into feature/AndroidByteRangeStream
Check if manifest item is null before attempting to use a filtered byte stream with it.