Add vendor (steam)

vendor/github.com/Philipp15b/go-steam/netutil/http.go

@@ -0,0 +1,17 @@
+package netutil
+
+import (
+	"net/http"
+	"net/url"
+	"strings"
+)
+
+// Version of http.Client.PostForm that returns a new request instead of executing it directly.
+func NewPostForm(url string, data url.Values) *http.Request {
+	req, err := http.NewRequest("POST", url, strings.NewReader(data.Encode()))
+	if err != nil {
+		panic(err)
+	}
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	return req
+}