async/await hack

[lastmjs]

Look into a simple transformation from async/await to generators, basically the transformations would look like this: async -> * and await -> yield.

Because our asynchronous code is currently limited to cross-canister calls, and we tightly control that functionality, it may be simple to do this replacement. Under the hood everything will be done with generators.

This hack could solve or make easier the following issues:

• Possibly collapse UpdateAsync into Update and QueryAsync into Query #359
• Improve TypeScript typechecking #138

This is also an easier stop-gap solution for #121

[lastmjs]

We have a few plausible paths forward to do this without a hack, so we are taking the idea of a hack off the table