Bump version to 0.4.0

appveyor.yml

 ---
 
-version: 0.3.1-{build}
+version: 0.4.0-{build}
 
 configuration: Release
 image: Visual Studio 2017

include/mtxclient/http/session.hpp

@@ -93,7 +93,7 @@ setup_headers(mtx::http::Session *session,
               const std::string &content_type       = "",
               const std::string &endpoint_namespace = "/_matrix")
 {
-        session->request.set(boost::beast::http::field::user_agent, "mtxclient v0.3.1");
+        session->request.set(boost::beast::http::field::user_agent, "mtxclient v0.4.0");
         session->request.set(boost::beast::http::field::accept_encoding, "gzip,deflate");
         session->request.set(boost::beast::http::field::host, session->host);