Function center

center(
    text?: null | string,
    width?: number,
    placeholder?: string,
): undefined | null | string
Returns a string that centers the given text using placeholder
Parameters
- Optionaltext: null | string
  the text to inspect
- width: number = -1
  the max width of the expected string
- placeholder: string = ' '
  the placeholder to pad
Returns undefined | null | string
a string that centers the given text using placeholder
Author
David Hsing
Example
```
center('foobar', -1);    // 'foobar'
center('foobar', 0);    // ''
center('foobar', 3);    // 'foobar'
center('foobar', 7);    // 'foobar '
center('foobar', 10);    // '  foobar  '
```