Added support for http-interop/http-middleware 0.5.0 (no BC Break)

[michalbundyra]

We keep also support for previous version. Now it depends on the library consumer what version of http-middleware to use. We accomplish that by using external library webimpress/http-middleware-compatibility.

Please note that tests runs with lowest/locked/latest dependencies. I've set composer.lock on http-middleware 0.4.1, lowest will be 0.1.1 and latest 0.5.0. All test pass :)

Probably we don't need support version http-middleware 0.1.1 anymore, so can add conflict condition in composer. To support it, I've added in two place method next as proxy to method handle (also new method, to support http-middleware 0.5.0) - and now process is proxy to handle.

Definitely we need update documentation a bit more. I'm thinking about all examples in documentation. How we should do that? Use always http-middleware interfaces (what version?) or aliases from webimpress/http-middleware-compatibility? IMHO, final library users should use http-middleware interfaces directly.

[michalbundyra]

Rebased and changed target to develop branch.

[weierophinney]

Thanks, @webimpress!