Refactor tests into new file and convert them to ert.

* Changelog: Use utf-8 coding.
* test.sh (cmd): require 'slime-tests instead of slime. Remove
trailing whitespace.
* slime-tests.el: new file.
* slime.el: move tests into slime-tests.el and convert them
to ert. Remove trailing whitespace.
Closes #43: slighter saner REPL prompt

* slime-repl.el: Remove trailing whitespace.
(slime-repl-mode-map): Don't clobber C-a and home.
(slime-repl-insert-prompt): emulate comint.el's properties,
so `slime-repl-bol' is no longer needed and `just-one-space'
works.
(slime-repl-bol): remove it.