Wrapper for AMD's OpenCL FFT.
Sadly not open sourced and the library uses version tags which prevents linking it to the NVidia OpenCL library installed with their Linux driver. Since the vendor-specific part is decoupled from this, we can use AMD's OpenCL library with NVidias driver though.
With clAmdFft 1.8.291 on NVidia hardware the result is completely wrong though...
see: http://www.bealto.com/gpu-fft2.html
from 2011-12-11 tarball. Public Domain.
Add argument for build option string
Add type traits to convert between vector versions of CL types.
Alternative OpenCL FFT implementation.
Based on Eric Bainville's, but replaces hard-coded kernels with a generator function to create arbitrary power-of-2 radixes (which should make it easier to add non-power-of-2s).
Supports n-dimensional transforms using transposition kernel based on NVIDIA sample.
FFT tests: verify against FFTw, benchmark against CuFFT
Merge branch 'master' of https://github.com/ddemidov/vexcl

Conflicts:
	examples/CMakeLists.txt
Merge branch 'fft'
link Boost to FFT examples, too
Don't need to check for C compiler
Compiles with default -stdlib=libstdc++, no need to change it. Users can still override.
Fix Clang errors, move operators to global namespace.
Fix Clang warnings
Review suggestions
remove stray file
Add License
Move UserFunction body to value level.
Prettier constructor, allows for dynamic user functions (mirroring behaviour of function pointers).
Can't use two complex objects in one expression, segfaults.
Add cl_scalar*cl_vector operators.
Helper trait to add scaling to expressions:
`expr * factor`, `factor * expr` and `expr / factor` return a new expression where the factor has been applied to the `scale` field.