builder: Add assets builder.

* haunt/builder/assets.scm: New file.
* Makefile.am (SOURCES): Add it.

Makefile.am

@@ -48,6 +48,7 @@ SOURCES =					\
   haunt/asset.scm				\
   haunt/site.scm				\
   haunt/html.scm				\
+  haunt/builder/assets.scm			\
   haunt/builder/atom.scm			\
   haunt/builder/blog.scm			\
   haunt/ui.scm					\

haunt/builder/assets.scm

@@ -0,0 +1,39 @@
+;;; 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:
+;;
+;; Static asset builder.
+;;
+;;; Code:
+
+(define-module (haunt builder assets)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-9)
+  #:use-module (ice-9 ftw)
+  #:use-module (ice-9 match)
+  #:use-module (haunt asset)
+  #:export (static-directory))
+
+(define* (static-directory directory #:optional (dest directory))
+  "Return a builder procedure that recursively copies all of the files
+in DIRECTORY, a file names relative to a site's source directory, and
+copies them into DEST, a prefix relative to a site's target output
+directory.  By default, DEST is DIRECTORY."
+  (lambda _
+    (directory-assets directory dest)))