Added post-merge hook to run update on merge.

This will case `make update` to run everytime there is a successful
merge. This will include everytime the is a non no-op merge. This *will
not run* if:

1. There is no changes.
2. There is a conflict in the merge.

Additionally the make install set will now sym link the post-merge hook.

bin/post-merge

@@ -0,0 +1,8 @@
+#!/bin/sh
+
+local_hook="$HOME"/.git_template.local/hooks/post-merge
+[ -f "$local_hook" ] && . "$local_hook"
+
+.git/hooks/ctags >/dev/null 2>&1 &
+
+make update

makefile

@@ -5,6 +5,7 @@ cmd_exist = $(shell (command -v $(1) 1>&2 >/dev/null && echo true || echo false)
 install: | init update
 
 init: vim_init tmux_init
+	@ ln -svf $(SRC_DIR)/bin/post-merge $(SRC_DIR)/.git/hooks/post-merge
 update: vim_update
 
 tmux_init: