refactor: relocate `devutil`?

[ycexiao]

Problem

There is a subpackage devutils in this repo. In diffpy.structure, it's devutils is moved out from the code distribution. We are not sure if we should do it in this repo.

Proposed solution

Move devutils to the top-level directory, like in diffpy.structure?

[ycexiao]

In diffpy.srreal, there is only one module tunePeakPrecision.py inside devutils, its docstring:

"""Tune the peak precision parameter so that PDFCalculator gives
equivalent results to diffpy.pdffit2.

Usage: tunePeakPrecision.py [qmax] [peakprecision] [createplot]
"""

In diffpy.structure, there is also only one module sgtbx_extra_groups.py inside devutils, its docstring:

"""Quick and extremely dirty script for generating code for SpaceGroup
that are defined in cctbx, but not in mmLib.  It was used to generate
module sgtbxspacegroups.

This is a utility script that should not be included with code
distribution.

Not to be included with code distributions.
"""

[ycexiao]

They seem to be extra scripts that can help the users do something. I think we should not include them in the src, but we can provide them in the documentation. Users can copy and paste these scripts when they need these scripts.

[ycexiao]

@sbillinge , do we want to relocate the devutil?

[sbillinge]

looking at these, and looking at the name devutils, I now understand that these were scripts that Pavol or someone wrote to do some task and they just wanted to keep them around in case they needed them again. With this in mind, they are not user-facing so we don't want them in the docs. We also don't need them in the src packages as they will never be imported as far as I can tell. So my suggestion would be, in each case, to move them somewhere outside the package but within hte repo. It would be nice if we always put them in the same place when they exist (perhaps a directory at the top level called devutils?) and put a lightweight README.md that just says something like, "Library of scripts used as part of the code develpment" or sthg like that.

Since it is in top-level directory in diffpy.structure, and that was my first instinct above, let's do that as a matter of course. If you would after you make the readme, please could you also put a PR into diffpy.structure adding the same readme to that devutils directory over there too? Thanks!