quit when tree is last buf, open on enter if dir or no file

plugin/tree.vim

@@ -4,11 +4,13 @@ let s:save_cpo = &cpo
 set cpo&vim
 
 let g:loaded_netrw = 1
-let g:loaded_netrwPlugin = 1 " Disable netrw
+let g:loaded_netrwPlugin = 1
 
 hi def link LuaTreePopup Normal
 
 au BufWritePost * lua require'tree'.refresh()
+au BufEnter * lua require'tree'.check_windows_and_close()
+au VimEnter * lua require'tree'.check_buffer_and_open()
 
 command! LuaTree lua require'tree'.toggle()