When --nth is used with a custom --delimiter, the last delimiter was
included in the search scope, forcing you to write the delimiter in
a suffix-match query. This commit removes the last delimiter from the
search scope.

  # No need to write 'bar,$'
  echo foo,bar,baz | fzf --delimiter , --nth 2 --filter 'bar$'

This can be seen as a breaking change, but I'm gonna say it's a bug fix.

Fix #3983

Close #4185

This option can be used to replace a sed or awk in the post-processing step.

  ps -ef | fzf --multi --header-lines 1 | awk '{print $2}'
  ps -ef | fzf --multi --header-lines 1 --accept-nth 2

This may not be a very "Unix-y" thing to do, so I've always felt that fzf
shouldn't have such an option, but I've finally changed my mind because:

* fzf can be configured with a custom delimiter that is a fixed string
  or a regular expression.
* In such cases, you'd need to repeat the delimiter again in the
  post-processing step.
* Also, tools like awk or sed may interpret a regular expression
  differently, causing mismatches.

You can still use sed, cut, or awk if you prefer.

Close #3987
Close #1323

Fix #4222

* Proper clean-up of caches
* Force rerender list after the action

Only requiring '-suffix in --exact mode is confusing and not
straightforward. Requiring '-prefix in --exact mode means that
the users can experience unintended mode switches while typing.

e.g.
     'it   -> fuzzy (many results)
     'it'  -> boundary (few results)
     'it's -> fuzzy (many results)

However, user who intends to input a boundary query should not be
interested in the intermediate results, and the number of matches
decreases as she types, so it should be okay.

On the other hand, user who does intend to type "it's" will be surprised
by the sudden decrease of the match count, but eventually get the right
result.

Close #3963