DevOps: Adopt PEP 621 and use pyproject.toml

PEP 621 introduces the `pyproject.toml` file which is now the
recommended way for defining a project with its build and install
dependencies. In addition, it allows to provide configuration for
various tools, such as tox, instead of using individual files for each
tool.

The `MANIFEST.in` file is no longer required since the build backend
`flit` will automatically include all files, except those explicitly
marked with `[tool.flit.sdist] exclude`.

The description is added to the `__init__.py` of the package and it is
marked as `dynamic` in the `pyproject.toml` which will automatically
fetch it from the package docstring.

aiida_nwchem/__init__.py

@@ -1,3 +1,3 @@
 # -*- coding: utf-8 -*-
-"""aiida-nwchem package"""
+"""The official AiiDA plugin for NWChem"""
 __version__ = '2.1.0'

pyproject.toml

@@ -1,3 +1,76 @@
+[build-system]
+requires = ['flit_core>=3.4,<4']
+build-backend = 'flit_core.buildapi'
+
+[project]
+name = 'aiida-nwchem'
+dynamic = ['description', 'version']
+authors = [
+    {name = 'The AiiDA team', email = 'developers@aiida.net'}
+]
+readme = 'README.md'
+license = {file = 'LICENSE.txt'}
+classifiers = [
+    'Development Status :: 4 - Beta',
+    'Framework :: AiiDA',
+    'License :: OSI Approved :: MIT License',
+    'Operating System :: POSIX :: Linux',
+    'Operating System :: MacOS :: MacOS X',
+    'Programming Language :: Python',
+    'Programming Language :: Python :: 3.6',
+    'Programming Language :: Python :: 3.7',
+    'Programming Language :: Python :: 3.8',
+    'Topic :: Scientific/Engineering'
+]
+keywords = ['aiida', 'workflows', 'nwchem']
+requires-python = '>=3.6'
+dependencies = [
+    'aiida-core[atomic_tools]>=1.2.1',
+    'numpy',
+]
+
+[project.urls]
+Source = 'https://github.com/aiidateam/aiida-nwchem'
+
+[project.optional-dependencies]
+docs = [
+    'sphinx',
+    'sphinxcontrib-contentui',
+    'sphinxcontrib-details-directive',
+    'sphinx-rtd-theme',
+    'sphinxcontrib-napoleon',
+]
+pre-commit = [
+    'pre-commit~=2.17',
+]
+tests = [
+    'pgtest~=1.3',
+    'pytest~=6.2',
+    'pytest-regressions~=1.0',
+]
+
+[project.entry-points.'aiida.calculations']
+'nwchem.nwchem' = 'aiida_nwchem.calculations.nwchem:NwchemCalculation'
+'nwchem.base' = 'aiida_nwchem.calculations.nwchem:NwchemBaseCalculation'
+
+[project.entry-points.'aiida.parsers']
+'nwchem.nwchem' = 'aiida_nwchem.parsers.nwchem:NwchemBaseParser'
+
+[project.entry-points.'aiida.workflows']
+'nwchem.base' = 'aiida_nwchem.workflows.base:NwchemBaseWorkChain'
+
+[tool.flit.module]
+name = 'aiida_nwchem'
+
+[tool.flit.sdist]
+exclude = [
+    '.github/',
+    'docs/',
+    'tests/',
+    '.gitignore',
+    '.pre-commit-config.yaml',
+]
+
 [tool.flynt]
 line-length = 120
 fail-on-change = true