Add workflow actions to build wheels for linux, macos, win32, and win64.

.github/workflows/python-package-linux.yml

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+name: Linux Package
+
+on:
+  push:
+    branches: [ master ]
+    paths:
+    - 'mahotas/mahotas_version.py'
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Python 3.6
+      uses: actions/setup-python@v2
+      with:
+        python-version: '3.6'
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install twine
+    - name: Build manylinux Python wheels
+      uses: RalfG/python-wheels-manylinux-build@v0.2.2-manylinux2010_x86_64
+      with:
+        python-versions: 'cp36-cp36m cp37-cp37m cp38-cp38'
+        build-requirements: 'numpy'
+    - name: Publish wheels to PyPI
+      env:
+        TWINE_USERNAME: ${{ secrets.PYPI_USERNAME }}
+        TWINE_PASSWORD: ${{ secrets.PYPI_PASSWORD }}
+      run: |
+        twine upload wheelhouse/*-manylinux*.whl

.github/workflows/python-package-macos.yml

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+name: macOS Package
+
+on:
+  push:
+    branches: [ master ]
+    paths:
+    - 'mahotas/mahotas_version.py'
+
+jobs:
+  build:
+
+    runs-on: macos-latest
+    strategy:
+      matrix:
+        python-version: [3.6, 3.7, 3.8]
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v2
+      with:
+        python-version: ${{ matrix.python-version }}
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install setuptools wheel twine numpy
+    - name: Build and publish
+      env:
+        TWINE_USERNAME: ${{ secrets.PYPI_USERNAME }}
+        TWINE_PASSWORD: ${{ secrets.PYPI_PASSWORD }}
+      run: |
+        python setup.py bdist_wheel
+        twine upload dist/*

.github/workflows/python-package-win32.yml

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+name: Windows Package (x86)
+
+on:
+  push:
+    branches: [ master ]
+    paths:
+    - 'mahotas/mahotas_version.py'
+
+jobs:
+  build:
+
+    runs-on: windows-latest
+    strategy:
+      matrix:
+        python-version: [3.6, 3.7, 3.8]
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v2
+      with:
+        architecture: 'x86'
+        python-version: ${{ matrix.python-version }}
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install setuptools wheel twine numpy
+    - name: Build and publish
+      env:
+        TWINE_USERNAME: ${{ secrets.PYPI_USERNAME }}
+        TWINE_PASSWORD: ${{ secrets.PYPI_PASSWORD }}
+      run: |
+        python setup.py bdist_wheel
+        twine upload dist/*

.github/workflows/python-package-win64.yml

@@ -0,0 +1,34 @@
+name: Windows Package (x64)
+
+on:
+  push:
+    branches: [ master ]
+    paths:
+    - 'mahotas/mahotas_version.py'
+
+jobs:
+  build:
+
+    runs-on: windows-latest
+    strategy:
+      matrix:
+        python-version: [3.6, 3.7, 3.8]
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v2
+      with:
+        architecture: 'x64'
+        python-version: ${{ matrix.python-version }}
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install setuptools wheel twine numpy
+    - name: Build and publish
+      env:
+        TWINE_USERNAME: ${{ secrets.PYPI_USERNAME }}
+        TWINE_PASSWORD: ${{ secrets.PYPI_PASSWORD }}
+      run: |
+        python setup.py bdist_wheel
+        twine upload dist/*