Update ndarray requirement from ^0.14 to ^0.15

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Updates the requirements on ndarray to permit the latest version.

Changelog

Sourced from ndarray's changelog.

Version 0.15.0 (2021-03-25)

New features

• Support inserting new axes while slicing by [@jturner314]. This is an example:

  let view = arr.slice(s![.., -1, 2..;-1, NewAxis]);

  rust-ndarray/ndarray#570

• Support two-sided broadcasting in arithmetic operations with arrays by [@SparrowLii]

  This now allows, for example, addition of a 3 x 1 with a 1 x 3 array; the operands are in this case broadcast to 3 x 3 which is the shape of the result.

  Note that this means that a new trait bound is required in some places when mixing dimensionality types of arrays in arithmetic operations.

  rust-ndarray/ndarray#898

• Support for compiling ndarray as no_std (using core and alloc) by [@xd009642] and [@bluss]

  rust-ndarray/ndarray#861 rust-ndarray/ndarray#889

• New methods .cell_view() and ArrayViewMut::into_cell_view that enable new ways of working with array elements as if they were in Cells - setting elements through shared views and broadcast views, by [@bluss].

  rust-ndarray/ndarray#877

• New methods slice_each_axis/_mut/_inplace that make it easier to slice a dynamic number of axes in some situations, by [@jturner314]

  rust-ndarray/ndarray#913

• New method a.assign_to(b) with the inverse argument order compared to the existing b.assign(a) and some extra features like assigning into uninitialized arrays, By [@bluss].

  rust-ndarray/ndarray#947

Enhancements

... (truncated)

Commits

• c7ae4eb 0.15.0
• 3e48234 Merge pull request #952 from rust-ndarray/update-complex
• 383ac0e TEST: Update dev-dependency itertools to 0.10
• 888c160 API: Update num-complex to 0.4
• 175b8f8 Merge pull request #951 from rust-ndarray/disconnect-blas-dependency
• 5b96f1d TEST: Remove ndarray build.rs and test-blas-openblas-sys feature flag
• f98e5c0 API: Drop direct blas-src dependency, update docs for blas integration
• fdbc884 Merge pull request #948 from rust-ndarray/neg-stride-constructors
• 67397ac Merge pull request #949 from rust-ndarray/rename-directories
• 5c6ff77 MAINT: Rename directories for misc and tests in the root
• Additional commits viewable in compare view

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