Added payload to the request build. This fixes #30.

[naroga]

As of right now, if one passes a payload on a request to react/http, such as the following:

curl -X POST http://<myurl>/ --data "{\"key\": \"value\"}" -H "Content-Type: application/json"

The payload is unreachable within the server. It won't be parsed as a querystring on RequestHeaderParser::parseRequest and will thus be discarded.

This can't happen, and I believe this PR fixes the issue.

It adds a new parameter to the Request constructor ($payload), at the end, with a default value (null), as a way to not break backwards compatibility with classes that may omit this parameter. It also adds a getPayload() method to the request.

[naroga]

Notice this leaves the queryString untouched in a way to allow even for GET requests with both a querystring and a payload. This allows even for some weirder requests, like the second elasticsearch example here.

[naroga]

This fixes #30.

[cboden]

This will only work for non-streamed requests. See this comment for buffering and reading the entire body for non-streamed requests.

[naroga]

Obsolete because of b36fb25