transpose degree n matrices

[Alex-Jordan]

This builds on #1216 (which builds on #1215). If #1216 is updated following feedback, I will update here too. Once #1216 is merged, this diff should be more manageable.

In addition to changes from #1216, this has:

• a slice method for a Matrix object. This produces a degree (n-1) Matrix from a degree n Matrix. You specify an index and a value for that index, and it produces the degree (n-1) Matrix that is thereby defined. This is currently only used as a helper for the update to transpose. It is similar to row and column methods, but more general. And always produces something of the next lower degree.
• to transpose a degree n Matrix, the word "transpose" is perhaps a misnomer. Instead you have some permutation of the index dimensions in mind. For the usual transpose of a degree 2 matrix, this is just the permutation (12). For a degree n matrix, you might want to permute the indices in a different way. Doing this once can make it more efficient to repeatedly access data in the Matrix, depending on the scenario. So now you can transpose a degree n Matrix. If you don't specify a permutation, the default is to just swap the last two indices. This will look like a regular transposition on each of the degree 2 matrices in the frontal slice. Otherwise, for the permutation you may specify a cycle in the form of an array reference, or a product of cycles in the form of an array reference of array references.

This is the last of the updates I wanted to do before adding new methods for setting elements, removing columns and rows and a submatrix that @pstaabp has in #1076. We should make sure new tools work with degree n Matrix objects as we add them. Unless it is for sure only appropriate for degree 2 matrices.

[pstaabp]

Looks good, but we should bring the test suite in soon. There was one in my branch that probably works for a lot of this, but should be update.

Although I'm guessing you have a number of problems that you've been testing with, it's more efficient to have the test suite.

I can get it working with this branch and put in a PR to this if you'd like.

[drgrice1]

I haven't tested this at all yet, but I see some code changes that are needed. Some things that perlcritic pointed out.