Add in-place variants of dimension-changing operations for dynamic-dimensional arrays

[jturner314]

The .remove_axis(), .insert_axis(), .into_subview(), and .slice_move() methods do not currently have in-place variants that change the number of dimensions, because for fixed-dimensionality arrays the type changes when changing the number of dimensions. However, dynamic-dimensional arrays do not have this limitation. It would be useful to have variants of these methods for dynamic-dimensional arrays that take &mut self instead of self as the argument.

See #425 for some discussion.

[bluss]

Thanks for filing these issues

[jturner314]

Status update:

• ~.remove_axis() has been deprecated, and we shouldn't add an in-place variant of it.~

• .insert_axis_inplace() (in-place variant of .insert_axis()) was added in #537.

• .index_axis_inplace() (in-place variant of .into_subview()) was added in #537.

• So, the only one we're missing is an in-place variant of .slice_move(). We'll leave .slice_inplace() deprecated for a while, then remove it, then wait a while, then add .slice_inplace() for IxDyn arrays that removes axes like .slice_move() does.