Make it possible to change buffer's properties

If you ever should feel the urge to change the properties of Startify's
scratch buffer, you can overwrite them via an autocmd. E.g.:

    autocmd FileType startify setlocal buftype= statusline=YEEHAW

References #6.

autoload/startify.vim

@@ -26,10 +26,9 @@ function! startify#insane_in_the_membrane() abort
   endif
 
   enew
-  setfiletype startify
-
   setlocal noswapfile nobuflisted buftype=nofile bufhidden=wipe
   setlocal nonumber nolist statusline=\ startify
+  setfiletype startify
 
   if v:version >= 703
     setlocal norelativenumber