migrate fully to meson build system

- drop old build system
- move shared include and source files to common directory
- drop "rc-" prefix from shared include and source files
- move executable-specific code to individual directories under src
- adjust top-level .gitignore file for new build system

This closes #489.

src/value/meson.build

@@ -0,0 +1,15 @@
+value_execs = [
+  'service_get_value',
+  'service_set_value',
+  'get_options',
+  'save_options',
+  ]
+
+foreach exec : value_execs
+  executable(exec,
+    ['value.c', misc_c, version_h],
+    include_directories: [incdir, einfo_incdir, rc_incdir],
+    link_with: [libeinfo, librc],
+    install: true,
+    install_dir: rc_bindir)
+endforeach

src/value/value.c

@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) 2016 The OpenRC Authors.
+ * See the Authors file at the top-level directory of this distribution and
+ * https://github.com/OpenRC/openrc/blob/HEAD/AUTHORS
+ *
+ * This file is part of OpenRC. It is subject to the license terms in
+ * the LICENSE file found in the top-level directory of this
+ * distribution and at https://github.com/OpenRC/openrc/blob/HEAD/LICENSE
+ * This file may not be copied, modified, propagated, or distributed
+ *    except according to the terms contained in the LICENSE file.
+ */
+
+#define SYSLOG_NAMES
+
+#include <sys/types.h>
+#include <sys/time.h>
+
+#include <errno.h>
+#include <ctype.h>
+#include <inttypes.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <string.h>
+#include <syslog.h>
+#include <time.h>
+#include <unistd.h>
+
+#include "einfo.h"
+#include "rc.h"
+#include "misc.h"
+
+const char *applet = NULL;
+
+int main(int argc, char **argv)
+{
+	bool ok = false;
+	char *service = getenv("RC_SVCNAME");
+	char *option;
+
+	applet = basename_c(argv[0]);
+	if (service == NULL)
+		eerrorx("%s: no service specified", applet);
+
+	if (argc < 2 || !argv[1] || *argv[1] == '\0')
+		eerrorx("%s: no option specified", applet);
+
+	if (strcmp(applet, "service_get_value") == 0 ||
+	    strcmp(applet, "get_options") == 0)
+	{
+		option = rc_service_value_get(service, argv[1]);
+		if (option) {
+			printf("%s", option);
+			free(option);
+			ok = true;
+		}
+	} else if (strcmp(applet, "service_set_value") == 0 ||
+	    strcmp(applet, "save_options") == 0)
+		ok = rc_service_value_set(service, argv[1], argv[2]);
+	else
+		eerrorx("%s: unknown applet", applet);
+
+	return ok ? EXIT_SUCCESS : EXIT_FAILURE;
+}