Aio-request

* [Circuit breaker](https://github.com/Pliner/aio-request/pull/65)

* [Basic repr implementation](https://github.com/Pliner/aio-request/commit/adaa4888c3d372fa65f3dd5eb6113ab68f46de24)

* Fix Request.update_headers, add Request.extend_headers [59](https://github.com/Pliner/aio-request/pull/59)

* Add Response.is_json property to check whether content-type is json compatible [58](https://github.com/Pliner/aio-request/pull/58)
* Tracing support [54](https://github.com/Pliner/aio-request/pull/54),
* [Configuration](https://github.com/Pliner/aio-request/commit/f0e1904f4d87daf7c242a834168c0f1b25dd86d5) of a new pipeline