Add Code mobject with syntax highlighting

[YishiMichael]

Motivation

Add Code mobject with syntax highlighting. It's inherited from Text with the help of pygments, which is a python site-package and should be additionally installed.

Proposed changes

• Rewrite Text.text2settings() method so that substrings specified in t2f, t2s, t2w can occupy each other.
• Add Code mobject with the code highlighted, which supports different languages and various styles.

Test

Code:

from manimlib import *


EXAMPLE_HELLO_WORLD_CODE_DICT = {
"python": """
print("Hello World!")
""",

"C++": """
# include <iostream>

using namespace std;

int main() {
    cout << "Hello World!" << endl;
    return 0;
}
""",

"Java": """
public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello World!");
    }
}
""",

"C": """
# include <stdio.h>

int main() {
    printf("%s\\n", "Hello World!");
    return 0;
}
"""
}


class CodeExampleScene(Scene):
    def construct(self):
        code_mobs = VGroup(*[
            Code(EXAMPLE_HELLO_WORLD_CODE_DICT[lang], language=lang, code_style=code_style)
            for lang, code_style in zip(
                ["python", "C++", "Java", "C"],
                ["zenburn", "monokai", "algol", "emacs"]
            )
        ]).arrange_in_grid(2, 2, h_buff=0.0, v_buff=0.5)
        self.add(code_mobs)

Result: