Add Statistics Notebook (#617)

* Initial commit adding Statistics notebook

* Added basic plan for the structure of the example

* Added first draft example

* Added statistics to mkdocs.yml

* Clean up notebook

* Prettified output

Author: dchirst

docs/mkdocs.yml

@@ -59,6 +59,7 @@ nav:
       - Non-WebMercator TMS: "examples/notebooks/Working_with_nonWebMercatorTMS.ipynb"
       - NumpyTile: "examples/notebooks/Working_with_NumpyTile.ipynb"
       - Algorithm: "examples/notebooks/Working_with_Algorithm.ipynb"
+      - Statistics: "examples/notebooks/Working_with_Statistics.ipynb"
 
   - API:
     - titiler.core: