feat: adds vim.notify

Adds function to notify the user like this:
`:lua vim.notify("hello user")`
embeds log levels vim.log.levels.

you can then reassign vim.notify to for instance
```
function notify_external(msg, log_level, opts)
	vim.fn.jobstart({"notify-send", msg })
end
```

src/nvim/log.h

@@ -17,10 +17,11 @@
 #endif
 
 
-#define DEBUG_LOG_LEVEL 0
-#define INFO_LOG_LEVEL 1
-#define WARN_LOG_LEVEL 2
-#define ERROR_LOG_LEVEL 3
+#define TRACE_LOG_LEVEL 0
+#define DEBUG_LOG_LEVEL 1
+#define INFO_LOG_LEVEL 2
+#define WARN_LOG_LEVEL 3
+#define ERROR_LOG_LEVEL 4
 
 #define DLOG(...)
 #define DLOGN(...)