Well maintained alternative

[Helveg]

Not to throw too much shade here, but it seems like there's not a lot of love and attention going to this repo, so I forked it, polished it, and rereleased it as sendpulse-client. In case other people are looking for an alternative, I'm planning to maintain it on a volunteer basis. Other maintainers and open development is very welcome 😇

New features:

• ESM and TS version, with CommonJS support.
• Better types (typing everything as any is not "TypeScript support"); but still lacking detailed interfaces for most response objects, help appreciated.
• No need for .init call anymore.
• Dropped callbacks, used Promises.
• Support token expiration.
• No more hard dependency on a filesystem. I straight up removed token storage, it's a short lived token in memory that requires 0-effort to re-request should the application restart.
• The client is a class with methods now.
• Renamed methods to unified naming convention.
• Node.js and browser compatible (not that you'd usually want to use client id/secret in browser env, not sure if other OAuth2 flows are supported by SendPulse, but just in case)

[mesbahdev1]

Good job!