prod: add types

[Beraliv]

• [ ] need to check if it's working

Connected to Issue#50

[Beraliv]

Two ways:

declare namespace SimpleScrollBar {
  export function initEl (element: Element): void;
  export function initAll (): void;
  export function moveBar (e: Event): void;
}

export default SimpleScrollBar;

or

export default interface SimpleScrollBar {
  initEl (element: Element): void;
  initAll (): void;
  moveBar (e: Event): void;
}

[Beraliv]

@buzinas what do you think about adding TS?

[Beraliv]

ping @buzinas what do you think?

[buzinas]

Thanks for your contribution! Sorry for taking so long to merge this.