core: Promise + Async / await library

[Cassolette]

❗ To keep things in one place I opened the issue in this repository, but this should be moved later. ❗

Hoping to introduce a Promise library in TFM Lua, and later on posssibly bundle a async/await library.

The async await library aims to be familiar with Javascript users, keeping code straightforward with error paths handled neatly. Using coroutines in Lua, this should be somewhat implementable to an extent.

• Promise lib
• Async-Await lib

[Cassolette]

After some consideration, I have decided to implement the Promise and Async-Await lib separately, and even consider leaving out the Promise lib completely. There are some overhead concerns with the way JS implements it by creating a Promise wrapper when async syntax is used.

Unlike Javascript, we have the benefit of not worrying about backward compatibility (yet). It also trims down technical complexity and standardises the way we write async code here.