Shu Li

There is a new package [ProteinSecondaryStructures.jl](https://github.com/m3g/ProteinSecondaryStructures.jl). Is it possible to add the support for secondary structure information based on it?

[ProteinSecondaryStructures.jl](https://github.com/m3g/ProteinSecondaryStructures.jl) is based on [PDBTools.jl](https://github.com/m3g/PDBTools.jl). Maybe we can directly using DSSP_jll or STRIDE_jll and add a ss property to Residue.

@jgreener64 I made a PR https://github.com/BioJulia/BioStructures.jl/pull/43. Please check and let me know what can be improved. I am new to Julia development.

Current implementation is not consistent with mrcfile. In mrcfile, the shape of data should be `(nz, ny, nx)`. https://github.com/ccpem/mrcfile/blob/a0573b0ded494e4338839277570dc924c2ee512a/mrcfile/utils.py#L90 but in MRCFile.jl, the shape is `(nx, ny, nz)`.

It seems that there is no elegant way to handle it. It has been discussed in HDF5.jl, https://github.com/JuliaIO/HDF5.jl/blob/master/docs/src/index.md#language-interoperability-with-row--and-column-major-order-arrays https://github.com/JuliaIO/HDF5.jl/issues/785

My concern is that if we permuted the data array, then `read_mmap` is not meaningful, but it seems we can create a `view` https://docs.julialang.org/en/v1/base/arrays/#Base.view.

I see. `PermutedDimsArray` also creates a view for the original `AbstractArray`.