Add typings for promise-mem

[gndelia]

As I need to use promise-mem in a Typescript repo, It is better if we add the typings for it. I also added tsd to easily test that the types are correctly generated (as having some compile code that uses it). That way we can ensure types do not break if changed.

Version was incremented to 1.0.2

Process checklist

• Manual tests passed or not applicable.
• Automated tests added or not applicable.
• Documentation updated or not required.

Metrics

Actual effort: 1h