[boost] [context] new version - support for Win64

I've uploaded boost.context-0.3.0.zip to boost vault. The new version supports the context-/stack- swapping provided by the OS (ucontext ABI on UNIX, Fiber ABI on Windows) as well a fast context swapping (using assembler). supported platforms: i386, x86_64, arm, mips, ppc OS: UNIX, Windows (32 bit/64 bit) More details can be found in the documentation (included in the archive).