Initial kriging commit

This is the first step toward implementing the full kriging workflow in
one of the GSTools core packages (which is the Rust one in this case,
obviously). For now, only simple kriging on isotropic fields is
implemented. This commit also includes a few early pieces for the
CovModel implemented in the core package.

.github/workflows/main.yml

@@ -25,6 +25,8 @@ jobs:
           toolchain: stable
           override: true
           components: rustfmt, clippy
+      - name: Install Dependencies
+        run: sudo apt-get install -y build-essentials gfortran
       - uses: actions-rs/cargo@v1
         name: fmt
         with:
@@ -50,7 +52,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
         with:
-          python-version: '3.10'
+          python-version: "3.10"
           architecture: x64
       - name: Build Wheels
         uses: messense/maturin-action@v1
@@ -78,7 +80,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
         with:
-          python-version: '3.10'
+          python-version: "3.10"
           architecture: ${{ matrix.target }}
       - name: Install Rust Toolchain
         uses: actions-rs/toolchain@v1
@@ -110,7 +112,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
         with:
-          python-version: '3.10'
+          python-version: "3.10"
       - name: Install Rust toolchain
         uses: actions-rs/toolchain@v1
         with:
@@ -152,7 +154,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
         with:
-          python-version: '3.10'
+          python-version: "3.10"
           architecture: x64
       - name: Install dependencies
         run: |

.gitignore

@@ -1,2 +1,3 @@
 debug/
 target/
+*.png