autocomplete: keep showing function prototype after selection

[IAKOBVS]

Expected behaviour:

[bscan]

Funny timing, I was actually just working on this feature #24 . With the new parser I added last week (parser.ts), many more features that require parsing code are now possible. signatures.ts contains most of the relevant code, plus some modifications to parser.ts. Call signatures now show up when typing signatures and when hovering over the subroutine itself. There's a little more work I'd like to do before releasing this to vscode and npm, especially around caching parsing results. A review would certainly be helpful if you're interested. Thanks!

[bscan]

This feature seems to be fairly stable now. Thanks!