Re-organise to use a bare repo

Re-organise to use a bare repo, e.g.
https://www.atlassian.com/git/tutorials/dotfiles.

.zsh/configs/plugins.zsh

@@ -0,0 +1,14 @@
+if is_macos; then
+  source /usr/local/share/antigen/antigen.zsh
+elif is_linux; then
+  # antigen.zsh has been downloaded manually for now,
+  # see https://github.com/zsh-users/antigen/issues/659.
+  source $HOME/.antigen.zsh
+fi
+
+antigen bundle mollifier/cd-gitroot
+antigen bundle zsh-users/zsh-autosuggestions
+antigen bundle zsh-users/zsh-completions
+antigen bundle zsh-users/zsh-syntax-highlighting
+
+antigen apply