[Pas2js] Async, AWait

[Michael Van Canneyt]

On Sun, 31 May 2020, warleyalex via Pas2js wrote:

> Nice!
>
> The Sleep method is missing in pa2js! This method is very useful, I think it
> should live at sysutils unit.

A nice idea.

It can't live in sysutils, because it depends on web.pas (window object) 
and sysutils cannot depend on web.pas. 
I added a new unit 'webutils.pas' and I put it in that.

I have some other ideas for functions to add to this unit, and if you have more
ideas for utility routines for web.pas, please share them.

Michael.