Add new transpose_mem_order configuration argument to enable more flexible pencil memory layouts.

[romerojosh]

In cuDecomp, users currently have only two options for memory layout orders for their pencil data buffers:

1. [X, Y, Z] corresponding to transpose_axis_contiguous[axis] = false
2. a prescribed cyclically-permuted layout such that the memory is contiguous along the pencil axis when transpose_axis_contiguous[axis] = true (e.g., [Y, Z, X] for the Y-axis pencil).

This can limit the ease of application of cuDecomp to codes that have established their own memory orderings that do not match what is currently available.

This PR enables users to more flexibly set their own desired pencil buffer memory layouts by pencil axis via a new transpose_mem_order entry in the cudecompGridDescConfig structure. This new entry overrides the setting from transpose_axis_contiguous.

From the updated documentation:
Advanced users who require more flexibility in the memory layout of the pencil buffers can override the layouts available via
transpose_axis_contiguous by setting thetranspose_mem_order array in the configuration structure. This array enables
users to set arbitrary memory layout orders for the pencil buffers by axis. For example, a user can set this structure as follows to have pencil memory in [X, Y, Z] order for the X-pencil and [Z, Y, X] order for the Y- and Z-pencils:

In C++:

    config.transpose_mem_order[0][0] = 0;
    config.transpose_mem_order[0][1] = 1;
    config.transpose_mem_order[0][2] = 2;
    config.transpose_mem_order[1][0] = 2;
    config.transpose_mem_order[1][1] = 1;
    config.transpose_mem_order[1][2] = 0;
    config.transpose_mem_order[2][0] = 2;
    config.transpose_mem_order[2][1] = 1;
    config.transpose_mem_order[2][2] = 0;

In Fortran:

    config%transpose_mem_order(1, 1) = 1
    config%transpose_mem_order(2, 1) = 2
    config%transpose_mem_order(3, 1) = 3
    config%transpose_mem_order(1, 2) = 3
    config%transpose_mem_order(2, 2) = 2
    config%transpose_mem_order(3, 2) = 1
    config%transpose_mem_order(1, 3) = 3
    config%transpose_mem_order(2, 3) = 2
    config%transpose_mem_order(3, 3) = 1