Readline history preserves newlines

* guile-readline/ice-9/readline.scm (make-readline-port): Preserve
  newlines.  This preserves the semantics of history entries that
  contain until-end-of-line comments using `;'.
Update libgc URL in README.

* README: Update libgc URL.  Suggested by Ian Grant
  <ian.a.n.grant@googlemail.com>.