First step in refactoring old SIMD hash engine into a new compile-time SIMD capable closure engine based engine.
Mapped in std::thread::hardware_concurrency().
Implemented boost::afio::hash::hash_threadpool().
Added make_unique and replaced those bits of code using the C++11 form.
Merge branch 'master' into content_hashing_merge

Conflicts:
	boost/afio/afio.hpp
Fixed misalignment of op type problems.
Now overrides std::allocator<> rather than specific STL container types for Int128, Int256 etc.

BOOST_THREAD_PROVIDES_FUTURE_CTOR_ALLOCATORS now is turned on, and errors out if not turned on.

The future hash value per op now (finally!) correctly uses the appropriate aligned allocator. This was harder to do than expected.