jump and make stubs for arm64 (aarch64) for iOS ABI

Hello, Oliver.

I have implemented make and jump context trampolines for ARM64 architecture. Original stubs are not not suitable since ABI and instruction sets of armv7 and A64 are much different. I have tested these stubs on IPad Mini Retina and iPhone 6+ (compiled using Apple LLVM 5.1 (Xcode 5.1)), all unit tests passed successfully.

Feel free to ask any questions. And thank you for useful library!

## Resources
**ARMv8 instruction set**
http://www.element14.com/community/servlet/JiveServlet/previewBody/41836-102-1-229511/ARM.Reference_Manual.pdf

**AArch64 Procedure call standard**
http://infocenter.arm.com/help/topic/com.arm.doc.ihi0055b/IHI0055B_aapcs64.pdf