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

首先查看 processing-examples 中的官方 sketch，以及 Processing.py 的 examples.py 中現有的子集，接著檢查 libprocessing 面向 Python 的入口點。在考量 issue 中所述語法差異的同時，系統地將這些範例移植到 Python；當官方範例集都有對應的 Python 版本時，即視為完成。