Use --depth option to avoid pulling devel branches

- fzf-tmux
- CTRL-T of bash/zsh/fish
    - fish implementation may not work if the path contains
      double-quote characters (FIXME)

Refactor shell extensions

- Use symlinks instead of generating the full content
- Update fish_user_paths and remove ~/.config/fish/functions/fzf.fish
- Create wrapper script for fzf when Ruby version and use it instead of
  exported function not to break fzf-tmux

When 1 is given, 50% of the screen width or height will be used as the
default size of the pane.

As they're made synchronous with the use of fzf-tmux script

[fzf-tmux] Allow opening fzf on any position (up/down/left/right)

The previous -w and -h will be synonyms for -r and -d respectively.

fzf-tmux -w -q q
fzf-tmux -w -- -q q

Add fzf-tmux script

This avoids the problem in which :FZF command silently fails when fzf
executable cannot be found in $PATH of the hosting tmux server.

/cc @Tranquility