Bake plan on creation
Input/Output specific to plan (so r2c/c2r conversion might be rolled into the first/last kernel)
Gnuplot compatible output format
Move kernel parameters into generators
Output performance in benchmark, FFTw run optional
Number of threads known at kernel compile time
Merge branch 'master' of https://github.com/ddemidov/vexcl

Conflicts:
	examples/fft_benchmark.cpp
	vexcl/fft.hpp
	vexcl/fft/kernels.hpp
	vexcl/fft/plan.hpp