Multiple Content Filter support (iteration + correct byte buffer passing)
see https://github.com/readium/readium-sdk/issues/147
Includes: zero'ed buffer in Filter Context for byte ranges, explicit type cast for seekable byte stream in non-range Content Filter, fixed memory free() in media decryption with byte-range support, refactored vector of pairs (generic tuple) in favour or 2x aligned vectors of concrete types (Filter + FilterContext), removed duplicate / unused method signatures, harmonised tab vs. spaces.