Types do not include Promise<>

[chrisvander]

Making use of this package in a TypeScript project, inside of a WebWorker. At import, the GLPK type does not indicate it's a promise, nor does the result of glpk.solve, so at the moment I am typecasting to unknown and then the Promise<> type. Could you fix this?

[jvail]

Would you like to propose a change or file a PR? I do not have a browser ts project where I import glpk.js. Also I am not sure if there should be an index.d.ts file and then how to share types with glpk.d.ts...