Vc going for 1.0

[Matthias Kretz]

Hi all,

I'm finally (sorry, this took way too long) on track for releasing Vc 1.0.

The most important changes are:

* AVX (u)int_v is now only one SSE width instead of the full AVX width.

* AVX2 support added with doubled width for (u)int_v and (u)short_v.

* Xeon Phi support (Knights Corner). This requires an Intel compiler.

* Dropped the guarantee of (u)int_v::size() == float_v::size(). Therefore, the 
implicit conversion between int and float vectors present in Vc 0.x is ill-
formed with 1.0.

* New simd_cast<T> cast function. It allows arbitrary conversions from one or 
more Vectors/SimdArrays to one or more Vectors/SimdArrays.

* New simdize<T> expression "vectorizes T". This is still somewhat 
experimental.

* sfloat_v is gone in favor of a generic SimdArray<T, N> class template 
allowing you to build vector objects of arbitrary width. Thus, to get the old 
sfloat_v type back you'd write 'using sfloat_v = Vc::SimdArray<float, 
Vc::short_v::size()>;'. SimdArray is not meant to be used as a container, i.e. 
N should be "small".

* Besides Vc::Vector<T> you can also now directly use microarchitecture 
specific types, such as Vc::SSE::Vector<T>. This enables you to use SSE 
vectors and AVX vectors in the same translation unit. You should prefer 
SimdArray<T, N> in most cases, though.

* In Vc 0.x the Vector<T> class template was defined multiple times in 
different namespaces. Now it's a single class template Vc::Vector<T, Abi> with 
aliases in the implementation namespaces. This enables you to write a function 
such as
  template <typename T, typename Abi> void f(Vc::Vector<T, Abi> x)
which matches any Vc Vector type, whether that's the Scalar implementation or 
an actual SIMD implementation.

* Gather & scatter received a new interface that is a lot more intuitive and 
flexible. Use Vc::vector and/or Vc::array as alternatives to std::vector and 
std::array to get an additional subscript overload accepting Vc::Vector 
objects as argument to the subscript operator for gather & scatter.

* Requires C++11. Thus, many older compiler versions and, at least for now, 
MSVC are not supported anymore.

* More stuff I didn't think of right now.

If you are interested in using Vc 1.0 in your project soon I recommend you 
check out current Vc master and check out whether it works for you. There are 
still a few remaining issues, especially with the Intel compiler that will 
need to get fixed for the final 1.0 release.
Please report any issues you find on https://github.com/VcDevel/Vc/issues/new

Cheers,
	Matthias