Factor out time keeping code into its own module: mono_time.c.

It turns out, `unix_time` is also monotonic, and is used as such, so I've
renamed the new functions to `mono_time_*`.

2018-07-08:
```
00:01 <@irungentoo> the idea used to be that the unix_time() function
  could go backward in time but I think I might have started using it like
  if it could not after I changed it so that it would never go back in time
```

1 files changed, 35 insertions, 0 deletions

diff --git a/toxcore/mono_time.h b/toxcore/mono_time.h
new file mode 100644
index 00000000..63e0f49d
--- /dev/null
+++ b/toxcore/mono_time.h
@@ -0,0 +1,35 @@
+#ifndef C_TOXCORE_TOXCORE_MONO_TIME_H
+#define C_TOXCORE_TOXCORE_MONO_TIME_H
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct Mono_Time Mono_Time;
+
+Mono_Time *mono_time_new(void);
+void mono_time_free(Mono_Time *monotime);
+
+void mono_time_update(Mono_Time *monotime);
+uint64_t mono_time_get(const Mono_Time *monotime);
+bool mono_time_is_timeout(const Mono_Time *monotime, uint64_t timestamp, uint64_t timeout);
+
+// TODO(#405): Use per-tox monotime, delete these functions.
+void unix_time_update(void);
+uint64_t unix_time(void);
+int is_timeout(uint64_t timestamp, uint64_t timeout);
+
+/* return current UNIX time in microseconds (us). */
+uint64_t current_time_actual(void);
+
+/* return current monotonic time in milliseconds (ms). */
+uint64_t current_time_monotonic(void);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif  // C_TOXCORE_TOXCORE_MONO_TIME_H