Add vim swap file support

.config/nvim/swap.vim

@@ -0,0 +1,20 @@
+" Protect changes between writes. Default values of
+" updatecount (200 keystrokes) and updatetime
+" (4 seconds) are fine
+set swapfile
+set directory^=~/.config/nvim/swap//
+
+" protect against crash-during-write
+set writebackup
+" but do not persist backup after successful write
+set nobackup
+" use rename-and-write-new method whenever safe
+set backupcopy=auto
+
+" consolidate the writebackups -- not a big
+" deal either way, since they usually get deleted
+set backupdir^=~/.config/nvim/backup//
+
+" persist the undo tree for each file
+set undofile
+set undodir^=~/.config/nvim/undo//