* Support 'application/graphql' POST requests for 'juniper_warp'
* Add integration tests for 'application/graphql' POST requests and revive HttpIntegration test suite for 'juniper_warp'
* Support 'application/graphql' POST requests for 'juniper_hyper' and run its tests for both sync and async versions
* Run integration tests for both sync and async versions of 'juniper_warp' and update its CHANGELOG
* Support 'application/graphql' POST requests for 'juniper_iron'
* Fix 'application/graphql' POST requests support for 'juniper_actix'
* Support 'application/graphql' POST requests in 'juniper_rocket' and 'juniper_rocket_async'
* Upd juniper's CHANGELOG
* Add subscriptions support on GraphiQL
Addresses #501
BREAKING CHANGE: `juniper::http::graphiql::graphiql_source` now requires
a second parameter
BREAKING CHANGE: `juniper_hyper::graphiql` now requires
a second parameter
BREAKING CHANGE: `juniper_iron::GraphiQLHandler::new` now requires
a second parameter
BREAKING CHANGE: `juniper_rocket::graphiql_source` now requires
a second parameter
BREAKING CHANGE: `juniper_warp::graphiql_filter` now requires
a second parameter
* Add test where graphiql subscriptions endpoint is not None
* Bump` juniper`, `juniper_codegen`, and `juniper_tests` versions.
* Bump integration crate requirements to include 0.10.0. `juniper_iron` gets a semver breaking version as it has a breaking change but `juniper_iron` does not.
* Move `juniper_rocket` changelog into one file. This aligns with `juniper_iron` and will be easier
to automate in the future.
* Let `juniper_warp` and `juniper_hyper` use `0.9.x` versions of Juniper. They don't rely on anything in 0.10.0 so don't require it.
