In cbdcbce01d we introduced a Tim
Pope-inspired Git template scheme that automatically ran `ctags`
asynchronously through a hook after certain source control operations.
This hook is bypassed if a user uses `<leader>ct` to reindex their tags
from within Vim.
This change binds `<leader>ct` to use a Vimscript function that will
identify if the `ctags` hook exists in the local repository and executes
it. The function falls back to existing functionality if the hook does
not exist. We are moving the function out of `vimrc` as a first step
toward breaking our Vim configuration up by topic area.
76aa931b77