Fixes regular expression to match <head> element

Issue: https://github.com/readium/readium-sdk/issues/136
Addresses https://github.com/readium/SDKLauncher-iOS/issues/38 (+ potentially other platforms as well)

...by ifdef-ing the CPUCacheUtils.h/c functionality (which requires satellite assembly code to provide the actual function symbols, which the compiler picks on a platform-specific basis).
See ENABLE_SYS_CACHE_FLUSH
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.
not sure why my previous commit removed the line breaks at end of file...restoring them
Merge branch 'develop' into feature/epub3Bindings