PE-5845 NC - Creating a group with diacritical marks (áéíóúäëïöüñçâê) 

Diacritics not displaying properly

There was unnecessary (slurp) call which converts stream resource to Java string.
And somewhere in this conversion diacritics is lost. This patch makes it so that
request body is not touched at all. Instead of asking for empty body, we are asking
for desired HTTP request method and comparing it with list of officially supported
HTTP methods in http://hc.apache.org/httpcomponents-client-ga/httpclient/apidocs/org/apache/http/client/methods/HttpEntityEnclosingRequestBase.html
@MichalBryxi now I realized that this is not needed any more and could be simply passed as (:body req) as the buffering is processed in clj-http-client (in our proposed changes). So, the io namespace can go away (wow!).