Add --log-directory option

For specifying directory path in which to save automatically named log
files.

src/misc.c

@@ -24,6 +24,7 @@
 #include <stdlib.h>
 #include <unistd.h>
 #include <string.h>
+#include <sys/stat.h>
 #include <time.h>
 #include <errno.h>
 #include "error.h"
@@ -70,3 +71,19 @@ int ctrl_key_code(unsigned char key)
 
     return -1;
 }
+
+bool fs_dir_exists(const char *path)
+{
+    struct stat st;
+
+    if (stat(path, &st) != 0)
+    {
+        return false;
+    }
+    else if (!S_ISDIR(st.st_mode))
+    {
+        return false;
+    }
+
+    return true;
+}