Add support for Skribe document format.

* haunt/skribe.scm: New file.
* haunt/skribe/utils.scm: New file.
* haunt/reader/skribe.scm: New file.
* configure.ac: Check for guile-reader.
* Makefile.am (SOURCES): Add Skribe modules when guile-reader is
  available.
* example/haunt.scm: Include Skribe reader.
* example/posts/baz.skr: New file.
* README.md ("Requirements"): Mention guile-reader as optional dependency.

haunt/reader/skribe.scm

@@ -0,0 +1,44 @@
+;;; Haunt --- Static site generator for GNU Guile
+;;; Copyright © 2015 David Thompson <davet@gnu.org>
+;;;
+;;; This file is part of Haunt.
+;;;
+;;; Haunt 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.
+;;;
+;;; Haunt 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 Haunt.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+;;
+;; Skribe post reader.
+;;
+;;; Code:
+
+(define-module (haunt reader skribe)
+  #:use-module (haunt reader)
+  #:use-module (haunt skribe)
+  #:use-module (haunt skribe utils)
+  #:use-module (haunt utils)
+  #:export (make-skribe-reader
+            skribe-reader))
+
+(define* (make-skribe-reader #:key (modules '((haunt skribe utils))))
+  "Return a new Skribe post reader that imports MODULES by default
+before reading a document."
+  (make-reader (make-file-extension-matcher "skr")
+               (lambda (file)
+                 (let ((file (absolute-file-name file)))
+                   (save-module-excursion
+                    (lambda ()
+                      (set-current-module (make-user-module modules))
+                      (load file %skribe-reader)))))))
+
+(define skribe-reader (make-skribe-reader))