fix: import error for parsers

[ycexiao]

Problem

Running pytest for diffpy.pdfmorph in the main branch.

FAILED tests/test_pdfmorphapp.py::TestApp::test_parser_systemexits - AttributeError: module 'diffpy.utils.parsers' has no attribute 'loaddata'
FAILED tests/test_pdfmorphapp.py::TestApp::test_morphsequence - AttributeError: module 'diffpy.utils.parsers' has no attribute 'loaddata'
FAILED tests/test_pdfmorphio.py::TestApp::test_morph_outputs - AttributeError: module 'diffpy.utils.parsers' has no attribute 'loaddata'
FAILED tests/test_tools.py::TestTools::test_field_sort - AttributeError: module 'diffpy.utils.parsers' has no attribute 'loaddata'

It comes from diffpy.pdfmorph tools.py

import diffpy.utils.parsers as parsers 
# ...
rv = parsers.loaddata.loadData(fname, unpack=True) 

The problem is related to diffpy.utils's sub-package parsers. Old parser is reconstructed as a sub-package and loaddata is a module now.

Proposed solution

A similar structure found in other projects under diffpy.
e.g. for diffpy.pdfmorph 's sub-package morph. The problem is avoided by importing the package's modules in its __init__.py.

from diffpy.pdfmorph.morphs.morph import Morph  # noqa: F401
from diffpy.pdfmorph.morphs.morphchain import MorphChain  # noqa: F401
# ...

Mirroring this method may solve the problem

[bobleesj]

@ycexiao

am a bit confused. If the API of 'loaddata' has been changed in diffpy.utils, why dont we import it using a new path?