Namespacing of functions / aliasing imports

[rkalis]

Right now, imports are full-file flat imports (import "./lib.cash"). That works fine on a small scale, but when people are publishing libraries to npm, it becomes harder to manage potential name collisions. That is why we want to allow aliasing/namespacing of imports, and also potentially only importing specific functions/globals from a file. See below:

// Alias imports + import specific functions
import { func1, func2 as funcX } from "./lib.cash";

// Alias the entire import (accessed as Lib.func1(...)
import * as Lib from "./lib.cash"
// Alternative syntax
import "./lib.cash" as Lib;

(created from #369)