Add vim defer plugin

vim/plugin/defer.vim

@@ -0,0 +1,10 @@
+function Defer(command, callback)
+  let l:buffer = []
+  call job_start(a:command, {
+  \ "out_io": "pipe",
+  \ "out_cb": { pipe, text -> add(l:buffer, text) },
+  \ "close_cb": { pipe -> a:callback(l:buffer) }
+  \ })
+endfun
+
+comm -nargs=* Defer call Defer(<q-args>, { buffer -> 0 })