We want to create a function that will add numbers together when called in succession.
```ts
add(1)(2); // == 3
```
We also want to be able to continue to add numbers to our chain.
```ts
add(1)(2)(3); // == 6
add(1)(2)(3)(4); //  == 10
add(1)(2)(3)(4)(5); // == 15
```
and so on.

A single call should be equal to the number passed in.
```ts
add(1); // == 1
```
We should be able to store the returned values and reuse them.
```ts
var addTwo = add(2);
addTwo; // == 2
addTwo + 5; // == 7
addTwo(3); // == 5
addTwo(3)(5); // == 10
```
We can assume any number being passed in will be valid whole number.