Add Listings API

[James Turner]

API: https://docs.dev.to/api/#tag/listings

For implementing it, you can use my ArticleService class as a guide and create an appropriate interface like how I have IArticleApi. The ApiService class provides the helper methods for constructing the requests for GET and PUT.

[Facundo Giuliani]

Can I work on this one?

[James Turner]

Yep - sure thing!