Provide Ivy commands for Purpose. Features: - make Purpose use Ivy interface when `ivy-mode' is on - special ivy commands: + `ivy-purpose-switch-buffer-with-purpose': same as `ivy-switch-buffer', but only list buffers with a specific purpose (default: same purpose as current buffer). + `ivy-purpose-switch-buffer-with-some-purpose': choose a purpose, then call `ivy-purpose-switch-buffer-with-purpose'. + `ivy-purpose-switch-buffer-without-purpose': same as `ivy-switch-buffer', but ignore Purpose when displaying the buffer. Setup: Call `ivy-purpose-setup' in your init file. It will "Ivy-fy" Purpose commands, but won't change any key bindings. Alternatively, you can set `purpose-preferred-prompt' to `vanilla' instead. Key Bindings: `ivy-purpose' doesn't bind any keys, you are free to define your own bindings as you please.