Modernize build system to use setup.cfg

For now, keep but deprecate the requirements/*.txt files.

setup.cfg

@@ -1,8 +1,101 @@
+[metadata]
+name = ocrmypdf
+description = OCRmyPDF adds an OCR text layer to scanned PDF files, allowing them to be searched
+long_description = file: README.md
+long_description_content_type = text/markdown; charset=UTF-8
+url = https://github.com/jbarlow83/OCRmyPDF
+author = James R. Barlow
+author_email = james@purplerock.ca
+license_files = 
+    LICENSE
+keywords =
+    PDF
+    OCR
+    optical character recognition
+    PDF/A
+    scanning
+classifiers =
+    Programming Language :: Python :: 3.6
+    Programming Language :: Python :: 3.7
+    Programming Language :: Python :: 3.8
+    Programming Language :: Python :: 3.9
+    Development Status :: 5 - Production/Stable
+    Environment :: Console
+    Intended Audience :: End Users/Desktop
+    Intended Audience :: Science/Research
+    Intended Audience :: System Administrators
+    License :: OSI Approved :: Mozilla Public License 2.0 (MPL 2.0)
+    Operating System :: MacOS :: MacOS X
+    Operating System :: Microsoft :: Windows :: Windows 10
+    Operating System :: POSIX
+    Operating System :: POSIX :: BSD
+    Operating System :: POSIX :: Linux
+    Topic :: Scientific/Engineering :: Image Recognition
+    Topic :: Text Processing :: Indexing
+    Topic :: Text Processing :: Linguistic
+project_urls =
+    Documentation = https://ocrmypdf.readthedocs.io/
+    Source = https://github.com/jbarlow83/ocrmypdf
+    Tracker = https://github.com/jbarlow83/ocrmypdf/issues
+
+[options]
+zip_safe = False
+packages = find:
+package_dir =
+    =src
+platforms = any
+include_package_data=True
+install_requires =
+    cffi >= 1.9.1  # must be a setup and install requirement
+    coloredlogs >= 14.0  # strictly optional
+    img2pdf >= 0.3.0, < 0.5  # pure Python, so track HEAD closely
+    pdfminer.six >= 20191110, != 20200720, <= 20201018
+    pikepdf >= 2.10.0
+    Pillow >= 8.2.0
+    pluggy >= 0.13.0, < 1.0
+    reportlab >= 3.5.66
+    setuptools
+    tqdm >= 4
+python_requires = >= 3.6
+setup_requires =  # can be removed whenever we can drop pip 9 support
+    cffi >= 1.9.1  # to build the leptonica module
+    setuptools_scm  # so that version will work
+    setuptools_scm_git_archive  # enable version from github tarballs
+
+[options.package_data]
+ocrmypdf =
+    data/sRGB.icc
+    py.typed
+
+[options.packages.find]
+where = src
+
+[options.extras_require]
+test =
+    pytest >= 6.0.0
+    pytest-xdist >= 2.2.0
+    pytest-cov >= 2.11.1
+    python-xmp-toolkit == 2.0.1  # also requires apt-get install libexempi3
+                                 # or brew install exempi
+docs =
+    sphinx
+    sphinx_rtd_theme    
+extended_test =
+    PyMuPDF == 1.13.4
+watcher =
+    watchdog >= 1.0.2, < 2
+webservice =
+    Flask >= 1, < 2
+
+[options.entry_points]
+console_scripts =
+    ocrmypdf = ocrmypdf.__main__:run
+
 [bdist_wheel]
 python-tag = py36
 
 [aliases]
-test=pytest
+test = pytest
 
 [check-manifest]
 ignore =
@@ -19,17 +112,14 @@ addopts =
 	-n auto
 
 [isort]
-multi_line_output=3
-include_trailing_comma=True
-force_grid_wrap=0
-use_parentheses=True
-line_length=88
+multi_line_output = 3
+include_trailing_comma = True
+force_grid_wrap = 0
+use_parentheses = True
+line_length = 88
 known_first_party = ocrmypdf
 known_third_party = PIL,_cffi_backend,cffi,flask,img2pdf,pdfminer,pikepdf,pkg_resources,pluggy,pytest,reportlab,setuptools,sphinx_rtd_theme,tqdm,watchdog,werkzeug
 
-[metadata]
-license_file = LICENSE
-
 [coverage:paths]
 source =
 	src/ocrmypdf