Fix #71: Add support for enabling/disabling services in /etc/finit.d

This patch adds support for enabling and disabling services in
/etc/finit.d/ by adding another subdirectory:

    /etc/finit.d/available

Enabled service/run/task stanzas are by convention symlinked
to the parent dir.  The initctl tool has three new convenience
commands to facilitate operating with this:

   initctl list
   initctl enable  <CONF>
   initctl disable <CONF>

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

src/serv.h

@@ -0,0 +1,38 @@
+/* List and enable/disable service configurations
+ *
+ * Copyright (c) 2017  Joachim Nilsson <troglobit@gmail.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#ifndef FINIT_SERV_H_
+#define FINIT_SERV_H_
+
+int serv_list    (char *arg);
+int serv_enable  (char *arg);
+int serv_disable (char *arg);
+
+#endif /* FINIT_SERV_H_ */
+
+/**
+ * Local Variables:
+ *  indent-tabs-mode: t
+ *  c-file-style: "linux"
+ * End:
+ */