v0.3.1

wgpu-nufft 0.3.1

C, Fortran, and MATLAB interfaces, and a first transform of a session as
quick as in 0.2.0; see CHANGELOG.md.

Added:

• wgpu-nufft-c (capi/): a C library declared by capi/include/wgpu_nufft.h.
  Plans of type 1, 2 and 3 in one to eight dimensions take host arrays, set
  their points once and run batches; one-call functions (wgpu_nufft1d1 to
  wgpu_nufft3d3) keep their plans for reuse. Double-precision arrays run in
  native f64 where the GPU supports it and in Df64 elsewhere, single-
  precision arrays in f32, and plans fall back to the CPU backend without a
  usable GPU.
• A Fortran module (fortran/wgpu_nufft.f90) over the C library, tested
  with gfortran and Intel ifx.
• A MATLAB interface (matlab/): one-call functions wgpunufft1d1 to
  wgpunufft3d3, the wgpunufft_plan class, and a MEX gateway for MATLAB
  R2018a or later, which build_wgpu_nufft compiles.

Fixed:

• Type-1 plans compile their spreading shaders when an execution first
  needs them, for the bin geometry it uses. 0.3.0 compiled two variants at
  plan creation, which made the first transform of a session slower than in
  0.2.0.

Known limitations:

• The MATLAB interface compiles and links but has not yet run in MATLAB.
• On DX12 with FXC, Df64 plans take minutes to create; on Windows, prefer
  Vulkan for Df64 plans.
• 7D and 8D plans are practical only on small grids at tolerances near
  1e-3.
• Metal has not been tested.