Add `random()` and `random_seed()`

From the random() reference page:

Generates random numbers. Each time the random() function is called, it returns an unexpected value within the specified range. If only one parameter is passed to the function, it will return a float between zero and the value of the high parameter. For example, random(5) returns values between 0 and 5 (starting at zero, and up to, but not including, 5).

If two parameters are specified, the function will return a float with a value between the two values. For example, random(-5, 10.2) returns values starting at -5 and up to (but not including) 10.2. To convert a floating-point random number to an integer, use the int() function.

From the randomSeed() reference page:

Sets the seed value for random(). By default, random() produces different results each time the program is run. Set the seed parameter to a constant to return the same pseudo-random numbers each time the software is run.

先从 issue 中链接的 random() 和 randomSeed() 参考页面开始，然后在 libprocessing 中找到对应的 Processing API 入口点。按照文档实现这两个函数，使其具有一个参数和两个参数时的行为，并产生使用种子时的确定性输出，然后验证所得 API 与这些示例一致。