Now the prompt will act like the default bash readline with emacs key
bindings, clear and delete word.
You can now also move left and right in the prompt to insert chars in
the middle of the prompt rather than having to delete your search term
and start again.
This will allow you to get the buffer the user was on when they invoked
an ivy command. This buffer is called the `origin` and you can access it
with `vim.ivy.origin()`.
