WIP: Support 0.6

[dlfivefifty]

This starts supporting 0.6. I've dropped 0.4 compatibility so that the f.(x) syntax can be used. Are we OK with this change? (I think @compat can restore 0.4 compatibility but I'm not sure it's worth it.)

the BigFloat FFT test fails for some reason:

Testing BigFloat support of FFT and DCT methods
Test Failed
  Expression: norm(ifft(fft(c)) - c) < 200 * (norm(c) * eps(BigFloat))
   Evaluated: 3.290907383297889365567835493403282408529556851637210612211926363351574968498589e-13 < 2.841706296661406868731913357740366307573017126122182078005142968265071086475453e-74
ERROR: LoadError: LoadError: There was an error during testing
while loading /Users/solver/.julia/v0.6/FastTransforms/test/fftBigFloattest.jl, in expression starting on line 9
while loading /Users/solver/.julia/v0.6/FastTransforms/test/runtests.jl, in expression starting on line 189

[dlfivefifty]

We can't merge this until we have a solution to JuliaLang/Compat.jl#312

[dlfivefifty]

As 0.5 compatibility is broken

[stevengj]

I'm confused by your bigfloat FFT test. Julia has never included a bigfloat FFT (if you pass it bigfloats, it converts to Float64). I had an rough PR for this at one point, but it was never merged.

[dlfivefifty]

Mikael implemented an FFT for BigFloats: FastTransforms/src/fftBigFloat.jl

[dlfivefifty]

The implementation would also work for other types... @stevengj do you think it would be worth creating an FFT.jl package and putting it there (until a more robust implementation is developed)?

[stevengj]

See also JuliaLang/julia#6193 for my bigfloat implementation, which also used Bluestein combined with radix-2 IIRC ... yes, but at some point the fft functionality is likely to be moved out of Base, so maybe that would be a better time to make an FFT package.

[MikaelSlevinsky]

I don't have an issue with this. The BigFloat FFT hasn't been optimized, but it has been useful from time to time.

[dlfivefifty]

This is actually a bug in Julia 0.6: JuliaLang/julia#20381

I can't work around it using colon: JuliaLang/julia#20382

[dlfivefifty]

The bug was fixed in 0.6 master