Correctly handle ~-expansion

[tom-seddon]

Shouldn't the shell do this for you? But clearly it doesn't in beeblink's case. I'm sure this used to work. Or maybe it never has, and I somehow never noticed/never got round to adding an issue.

See nodejs/node#684 - looks like Node won't change this.

There's a helper function that's been there for ages but never used, so maybe I did notice this at some point:

beeblink/server/utils.ts

Line 447 in fc0cc9c

export function getTildeExpanded(pathString: string): string {

- this would do as a first pass.

https://www.npmjs.com/package/untildify? Looks like it might not handle the ~USER syntax, so little current advantage to using this. Does this even matter?