Close #413

[bash-completion] Add nvim to f_cmds

Not relying on exit status for CTRL-R

Patch submitted by @robinro and @JackDanger
Close #403 #242 #241 #203

In the case that fzf-tmux returns a user-selected result but with a
non-zero exit status (which can happen if a function inside $PS1 returns
non-zero) this allows CTRL-R to continue working as expected.

Addresses #203 (Tranquility's comment)

This prevents fzf from missing SIGWINCH during startup which
occasionally happens with fzf-tmux

Close #400

/cc @xconstruct

Close #392

  usage: ./install [OPTIONS]

      --help               Show this message
      --bin                Download fzf binary only
      --all                Download fzf binary and update configuration files
                           to enable key bindings and fuzzy completion
      --[no-]key-bindings  Enable/disable key bindings (CTRL-T, CTRL-R, ALT-C)
      --[no-]completion    Enable/disable fuzzy completion (bash & zsh)
      --[no-]update-rc     Whether or not to update shell configuration files

Close #376

Trigger netrw autocommand when opening directory

Interrupt handling during execute action was not serialized and often
caused crash, failed to restore the terminal state.

* _fzf_complete is the helper function for custom completion
    * _fzf_complete FZF_OPTS ARGS
    * Reads the output of the source command instead of the command string
    * In zsh, you can use pipe to feed the data into the function, but
      it's not possible in bash as by doing so COMPREPLY is set from the
      subshell and thus nullified
* Change the naming convention for consistency:
    * _fzf_complete_COMMAND

e.g.

  # pass completion suggested by @d4ndo (#362)
  _fzf_complete_pass() {
    _fzf_complete '+m' "$@" < <(
      local pwdir=${PASSWORD_STORE_DIR-~/.password-store/}
      local stringsize="${#pwdir}"
      find "$pwdir" -name "*.gpg" -print |
          cut -c "$((stringsize + 1))"-  |
          sed -e 's/\(.*\)\.gpg/\1/'
    )
  }

  # Only in bash
  complete -F _fzf_complete_pass -o default -o bashdefault pass

While in bash you can externally register custom completion functions
using `complete` command, it was not possible to do so in zsh without
changing completion.zsh as the name of the supported commands are
hard-coded within the code (See #362). With this commit, fzf-completion
of zsh will first look if `_fzf_COMMAND_completion` exists and calls the
function, so one can externally define completion functions for specific
commands.

This commit also tries to make the interface of (yet undocumented)
_fzf_list_completion helper function consistent across bash and zsh.

So the following code works both on bash and zsh.

    _fzf_pass_completion() {
      local pwdir=${PASSWORD_STORE_DIR-~/.password-store/}
      local stringsize="${#pwdir}"
      let "stringsize+=1"
      _fzf_list_completion '+m' "$@" << "EOF"
        find "$pwdir" -name "*.gpg" -print | cut -c "$stringsize"- | sed -e 's/\(.*\)\.gpg/\1/'
    EOF
    }

    # Only on bash
    complete -F _fzf_pass_completion -o default -o bashdefault pass

Note that the suggested convention and the interface are not yet final
and subject to change.

/cc @d4ndo

This change improves sort ordering for aligned tabular input.
Given the following input:

    apple   juice   100
    apple   pie     200

fzf --nth=2 will now prefer the one with pie. Before this change fzf
compared "juice   " and "pie     ", both of which have the same length.

Remove dependency on zsh/pcre module

Fixes #363.