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, 1 insertions, 1 deletions

diff --git a/testing/av_test.c b/testing/av_test.c
index 5cc3b5dd..87a01871 100644
--- a/testing/av_test.c
+++ b/testing/av_test.c
@@ -45,7 +45,7 @@ extern "C" {
 #include "../toxav/ring_buffer.c"
 
 #include "../toxav/toxav.h"
-#include "../toxcore/network.h" /* current_time_monotonic() */
+#include "../toxcore/mono_time.h" /* current_time_monotonic() */
 #include "../toxcore/tox.h"
 #include "../toxcore/util.h"