feat: write headers correctly

src/serve.fnl

@@ -1,4 +1,5 @@
 (local {:listen new-server} (require :http.server))
+(local {:new new-headers} (require :http.headers))
 (local {: dofile} (require :fennel))
 (local {: info} (require :log))
 
@@ -7,8 +8,12 @@
 (fn on-stream [_server stream]
   (stream:get_headers)
   (info "received request")
-  (stream:write_headers {:status 200})
-  (stream:write_body_from_string :hi))
+  (stream:write_headers (doto (new-headers)
+                              (: :append ::status :200)
+                              (: :append :content-type :application/json))
+                        false)
+  (stream:write_chunk "{}" true))
+
 (local server 
   (assert (new-server
             {:onstream on-stream