Implement ImplicitFunction

[YishiMichael]

Motivation

Implement ImplicitFunction class using isosurfaces package. This is borrowed from manim community edition.

Proposed changes

• M manimlib/mobject/functions.py: implement ImplicitFunction
• M requirements.txt: add dependency
• M setup.cfg: add dependency

Test

Code:

class FuncTest(Scene):
    def construct(self):
        graph = ImplicitFunction(
            lambda x, y: x * y ** 2 - x ** 2 * y - 2,
            color=YELLOW
        )
        self.add(NumberPlane(), graph)

Result:

[3b1b]

Nice, thank you!