* geesh/built-ins/echo.scm: New file.
* geesh/built-ins.scm: New file.
* Makefile.scm: Add them.
* geesh/shell.scm (exec-let): Include built-ins in command search.
* tests/shell.scm: Add a test for this.
* geesh/parser.scm: New file.
* tests/parser.scm: New file.
* Makefile.am: Add them.
* .dir-locals.el: New file. Include indenting rules for Shell AST
forms and 'call-with-backquoted-input-port'.