Close #175

So that it can be used with the recent Vim plugin although extra key
bindings are not available

Updates MacVim wiki link in README

Prepending can be problematic when the user install fzf using Homebrew,
execute the install script, and later upgrade fzf with Homebrew, and do
not rerun the install script. In that case, even though the homebrew
package is upgraded, the older version will still be used.

$fzf_base/man may not exist when installed with Homebrew.

    tree -C | fzf --ansi --tac

Use --depth option to avoid pulling devel branches