[Feather request] Make ic a function instead of an instance, to improve distinction and intuitiveness

[YunfangHou]

The ic is imported as an instance of IceCreamDebugger and function __call__ is invoked to print variable value in the console when the instance is initialized.

The problem is that:

1. In the user's IDE, ic will be highlighted in the color of instance/variable, not a function. It's not as visually recognizable as print, which is highlighted in the color of function, as shown in the image below.

2. IDE's auto completion will add parentheses after function automatically, but not for an instance or variable.
3. Invoking an instance is not as intuitive as invoking a function.

It would be better if there is an independent function which can be imported in the user's code.