[docs] Adds sphinx extensions

Steps to build the docs
```bash
cd docs
sphinx-apidoc -o . ../sagital_average
make html
python -m http.server -d _build/html# to load the automatically built documentation
```

Author: dpshelio

docs/conf.py

@@ -31,6 +31,10 @@
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
 extensions = [
+    'sphinx.ext.autodoc',  # Support automatic documentation
+    'sphinx.ext.coverage', # Automatically check if functions are documented
+    'sphinx.ext.mathjax',  # Allow support for algebra
+    'sphinx.ext.viewcode', # Include the source code in documentation
 ]
 
 # Add any paths that contain templates here, relative to this directory.