* geesh/environment.scm (*return-tag*): New variable.
(call-with-return): New public function.
(sh:return): New public function.
(*atexit*): New variable.
(*exiting?*) New variable.
(set-atexit!): New public function.
(sh:exit): New public function.
* geesh/repl.scm (run-repl): Call sh:exit at the end of a script.
* geesh/shell.scm (sh:exec-let): Use call-with-return for functions.
* geesh/built-ins/dot.scm (main): Use call-with-return.
* geesh/built-ins/utils.scm (get-evaluator): New public function.
* geesh/built-ins/dot.scm: New file.
* geesh/built-ins/eval.scm: New file.
* geesh/Makefile.am: Add them.
* geesh/built-ins.scm (*special-built-ins*): Add dot and eval.