Port the list of official examples to Python/libprocessing

The examples/demos that ship with the Processing Development Environment (PDE) are designed to cover the Processing API in a systematic way:

https://github.com/processing/processing-examples

Each sketch focuses on a specific function or feature. That makes them a useful baseline for checking feature parity.

This issue suggests porting the official examples to Python (mewnala).

Note: there is some prior work in Processing.py, but the syntax differs (camelCase), and only a relatively small subset of examples was ported:
https://github.com/jdf/processing.py/tree/master/examples.py

まず processing-examples にある公式スケッチと、Processing.py の examples.py にある既存のサブセットを確認し、その後 libprocessing の Python 向けエントリーポイントを調査します。Issue に記載されている構文の違いを考慮しながら、例を体系的に Python に移植します。公式の例のセットに対応する Python 版が揃えば完了です。