Closes #17: slime and (read-line) freeze

* slime-repl.el (slime-repl-read-mode): Closes #17: ignore
slime completion `slime-repl-read-mode-map'.
(slime-repl-read-mode-map): Put keymap in its own var.
Fix: slime-repl-delete-from-input-history saved back the old history entries before the in-memory ones.
Smarter slime-read-from-minibuffer: supports history and keymap.
Always jump to the prompt when navigating the repl history.
Smarter repl history navigation.

- M-r/M-s (or what slime-repl-previous/next-matching-input is bound to) can be used similar to C-s: when pressed multiple times then jumps to the next match with the same regexp

- minibuffer reading of regexp search has its own history, and defaults to the previous input

- pressing M-r while reading the regexp in the minibuffer initiates searching with the previous regexp (like isearch)

- only the sending of the repl input resets the index of navigation history

- drop the feature that the typed-in text at the repl is used as initial history search regexp (the new input method is much more flexible)

- while navigating, display in the minibuffer which repl history index we are at, and what regexp is used for filtering currently

- when reaching the most recent end of the history, then clear the repl input