feat(completion): switch from peco to fzf for command history completion

And also setup and configure fzf zsh plugins:

- ctrl+r searches shell history.
- ctrl+t searches for files and folders by name recursively within
  current directory while previewing highlighted item via less.
- alt+c recursively lists directories within current directory, and
  changes to the selected directory.

zsh/fzf.zsh

@@ -0,0 +1,18 @@
+#
+# fzf
+#
+
+export FZF_DEFAULT_OPTS="--bind=ctrl-k:kill-line --border=none --tabstop=4"
+export FZF_TMUX_HEIGHT=100%
+export FZF_TMUX=0
+export FZF_CTRL_T_OPTS="--preview='less {}'"
+
+# Install fzf binary from latest GitHub Release.
+zinit ice from'gh-r' as'program' pick'fzf'
+zinit light junegunn/fzf
+
+# Install fzf-tmux command and zsh plugins from default branch on GitHub.
+zinit ice from'gh' as'program' pick'bin/fzf-tmux' \
+  multisrc'shell/{completion,key-bindings}.zsh' \
+  id-as'junegunn/fzf-extras'
+zinit light junegunn/fzf