Added Async support

Thanks to @joelwurtz we now have an asynchronous client and a promise in the contract.

Our plugin architecture will use this functionality.

Initial alpha release

Yay, finally we got here.

After 7 months of work, we are proud to present our HTTP Client contract to the world.

Although this started as a project providing adapters to already existing HTTP Clients, the goal changed to a more general approach.

Initial release

This is the first preview release of the Http Adapter contract