Allow for customization of CTRL-R history listing

[pabloariasal]

• I have read through the manual page (man fzf)
• I have the latest version of fzf
• I have searched through the existing issues

Info

• OS
  • Linux
  • Mac OS X
  • Windows
  • Etc.
• Shell
  • bash
  • zsh
  • fish

Problem / Steps to reproduce

Currently the CTRL-R command used to print the history is hardcoded to fc -rl 1, which shows the default history listing containing the event number followed by a command.
The fact that the command is hardcoded and can't be modified hinders the ability to customize how history is displayed. For example, using history -E or fc -rld the history listing can be extended to show the time when the command was run and the corresponding exit code.

My suggestion is to introduce a FZF_CTRL_R_COMMAND variable (just like CTRL-T and ALT-C), that can be set by the users who want to customize history listing. I can create a PR if considered a valuable feature.

[junegunn]

Thanks for the suggestion, but I decided not to add more options to shell extensions. See my previous comment on the matter: #1492 (comment)

You might also want to see https://github.com/junegunn/fzf/search?q=FZF_CTRL_R_COMMAND&type=Issues