Consolidate timestamp implementation in one file

src/timestamp.h

@@ -0,0 +1,36 @@
+/*
+ * tio - a simple serial terminal I/O tool
+ *
+ * Copyright (c) 2014-2022  Martin Lund
+ *
+ * This program 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 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program 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 this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+#pragma once
+
+enum timestamp_t
+{
+    TIMESTAMP_NONE,
+    TIMESTAMP_24HOUR,
+    TIMESTAMP_24HOUR_START,
+    TIMESTAMP_24HOUR_DELTA,
+    TIMESTAMP_ISO8601,
+    TIMESTAMP_END,
+};
+
+char *timestamp_current_time(void);
+const char* timestamp_state_to_string(enum timestamp_t timestamp);
+enum timestamp_t timestamp_option_parse(const char *arg);