Add the colon built-in

* geesh/built-ins/colon.scm: New file.
* Makefile.am: Add it.
* geesh/built-ins.scm (*special-built-ins*): Add colon.

Makefile.am

@@ -43,6 +43,7 @@ check-spec:
 MODULES =                                       \
   geesh/built-ins/break.scm                     \
   geesh/built-ins/cd.scm                        \
+  geesh/built-ins/colon.scm                     \
   geesh/built-ins/continue.scm                  \
   geesh/built-ins/echo.scm                      \
   geesh/built-ins/export.scm                    \

geesh/built-ins.scm

@@ -33,7 +33,7 @@
 ;; Special built-ins take precedence over any other command.
 (define *special-built-ins*
   `(("." . ,undefined)
-    (":" . ,undefined)
+    (":" . ,(@@ (geesh built-ins colon) main))
     ("break" . ,(@@ (geesh built-ins break) main))
     ("continue" . ,(@@ (geesh built-ins continue) main))
     ("eval" . ,undefined)

geesh/built-ins/colon.scm

@@ -0,0 +1,28 @@
+;;; The Geesh Shell Interpreter
+;;; Copyright 2018 Timothy Sample <samplet@ngyro.com>
+;;;
+;;; This file is part of Geesh.
+;;;
+;;; Geesh is free software: you can redistribute it and/or modify
+;;; it under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation, either version 3 of the License, or
+;;; (at your option) any later version.
+;;;
+;;; Geesh is distributed in the hope that it will be useful,
+;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with Geesh.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (geesh built-ins colon))
+
+;;; Commentary:
+;;;
+;;; The 'colon' utility.
+;;;
+;;; Code:
+
+(define (main . args)
+  0)