* module/system/repl/common.scm (repl-prompt): Return a string instead of
outputting to the port, for better readline integration.
* module/system/repl/repl.scm (meta-reader, prompting-meta-read)
(start-repl): Integrate with (ice-9 readline) via the current-reader
fluid and the repl-reader function, both from boot-9.scm.
* module/system/repl/command.scm (system): Declare exports in the module
declaration.
* module/system/repl/repl.scm (start-repl): If the evaluation returns
multiple values, print them separately.
