Typescript types for SessionStore Promise based API support

[jonaskello]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the feature has not already been requested

🚀 Feature Proposal

In #78 the SessionStore was upgraded to support both callback and Promise based API. However this is not reflected in the current typescript types. I propose that the typescript types are updated to reflect the changes in #78.

Motivation

Typescript users could use Promise.

Example

No response

[mcollina]

Thanks for reporting! Would you like to send a Pull Request to address this issue? Remember to add unit tests. We use tsd for types