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.

先從 issue 中連結的 random() 和 randomSeed() 參考頁面開始，然後在 libprocessing 中找到對應的 Processing API 入口點。依照文件實作這兩個函式，使其具備一個參數和兩個參數時的行為，並產生使用種子時的確定性輸出，然後驗證所得的 API 與這些範例一致。