feat: Database.loadExtension

[eliassjogreen]

It seems to work locally at least with loading spatialite.

Example:

  import { Database } from "./mod.ts";

  const db = new Database("test.db", { loadExtensions: true });
  
  db.loadExtension("./mod_spatialite.dll");
  
  const [version] = db.prepare("select spatialite_version()").value<[string]>()!;
  console.log(version);
  
  db.close();

Implements #82

[DjDeveloperr]

LGTM. Few comments.
Also worth adding in doc.md

[DjDeveloperr]

LGTM, thanks!