* geesh/lexer.scm (get-parameter-expression): Use '#f' to signal an
omitted optional word instead of just omitting the word in the
resulting form.
* tests/lexer.scm: Add a test for omitted optional words.
* 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'.