Adds netifaces recipe, closes #239

Note this is an early version working on the `x86_64` simulator.
It wasn't tested on an arm device.
Requires setuptools to be installed:
```sh
python toolchain.py pip install setuptools
```
Tested with main.py:
```python
import netifaces
print("interfaces:", netifaces.interfaces())
```
And produced the following output in the `x86_64` simulator:
```
Available orientation: KIVY_ORIENTATION=LandscapeLeft LandscapeRight Portrait PortraitUpsideDown
Initializing python
Running main.py: /Users/vagrant/Library/Developer/CoreSimulator/Devices/.../Application/.../testnetifaces.app/YourApp/main.pyc
interfaces: ['lo0', 'gif0', 'stf0', 'en0', 'utun0', 'utun1']
Leaving
```

kivy_ios/recipes/netifaces/__init__.py

@@ -0,0 +1,48 @@
+import sh
+
+from os.path import join
+
+from kivy_ios.toolchain import CythonRecipe, cd, shprint
+
+
+class NetifacesRecipe(CythonRecipe):
+    """
+    Also requires `setuptools to be installed on target (for pkg_resources):
+    ```sh
+    python toolchain.py pip install setuptools
+    ```
+    """
+
+    version = "0.10.9"
+    url = "https://pypi.io/packages/source/n/netifaces/netifaces-{version}.tar.gz"
+    depends = ["python3", "host_setuptools3"]
+    library = "libnetifaces.a"
+    cythonize = False
+
+    def dest_dir(self):
+        return join(self.ctx.dist_dir, "root", "python3")
+
+    def get_netifaces_env(self, arch):
+        build_env = arch.get_env()
+        build_env["PYTHONPATH"] = join(
+            self.dest_dir(), "lib", "python3.8", "site-packages"
+        )
+        return build_env
+
+    def install(self):
+        arch = list(self.filtered_archs)[0]
+        build_dir = self.get_build_dir(arch.arch)
+        build_env = self.get_netifaces_env(arch)
+        hostpython = sh.Command(self.ctx.hostpython)
+        with cd(build_dir):
+            shprint(
+                hostpython,
+                "setup.py",
+                "install",
+                "--prefix",
+                self.dest_dir(),
+                _env=build_env,
+            )
+
+
+recipe = NetifacesRecipe()