Implement Yash autocompletion and keybinds

[unrealapex]

Similar to how Bash, Zsh, and Fish have completion and keybind files, this issue is a request to add completion and keybinds for the Yash shell.

magicant/yash#76

[unrealapex]

Yash does not currently support executing programs on key. Would there be any way to implement FZF's Ctrl + T keybind with this constraint? This function is the closest emulation but is still less convenient using than pressing Ctrl + T.

# example usage
#
# vi $(t)
t() {
  fzf -m --reverse --walker=file,dir,follow,hidden --scheme=path --height=40%
}