Program to find Factorial of number.

All returns `true` if all of the strings in the slice satisfy the predicate `f`.

Any returns `true` if one of the strings in the slice satisfies the predicate `f`.

variadic functions.

Filter returns a new slice containing all strings in the slice that satisfy the predicate `f`.

Include returns `true` if the target string t is in the slice.

Index returns the first index of the target string `t`, or -1 if no match is found.

Map returns a new slice containing the results of applying the function `f` to each string in the original slice.

function Literal Count prints the number of times it has been invoked.

variadic functions - functions which support any no.

Sphere - Volume function takes a function as a argument.

Sphere - Volume function returns an anonymous function.

Decorator design pattern - passing func as argument.