Requiring python 3.8. Using tkinter_gl source rather than wheel.

.github/workflows/linux.yml

@@ -31,7 +31,7 @@ jobs:
             pip install git+https://github.com/3-manifolds/PLink &&
             pip install git+https://github.com/3-manifolds/snappy_manifolds &&
             pip install git+https://github.com/3-manifolds/Spherogram &&
-            pip install https://files.pythonhosted.org/packages/1d/b8/a2e2979750527f291d6e181172e08495ebb65374ee7fbfbfc4fe33094532/tkinter_gl-1.0a2-py3-none-any.whl
+            pip install git+https://github.com/3-manifolds/tkinkter_gl
           CIBW_REPAIR_WHEEL_COMMAND_LINUX: auditwheel repair --strip -w {dest_dir} {wheel}
           CIBW_TEST_COMMAND: python -m snappy.test --skip-modern-opengl
 

setup.py

@@ -559,7 +559,7 @@ def add(self, source_file, dependency_mod_time=0.0):
 setup( name = 'snappy',
        version = version,
        zip_safe = False,
-       python_requires = '>=3',
+       python_requires = '>=3.8',
        install_requires = install_requires,
        packages = ['snappy', 'snappy/manifolds', 'snappy/twister',
                    'snappy/snap', 'snappy/snap/t3mlite', 'snappy/snap/peripheral',