Added argument parser and set all logs to STDERR

utils.h

@@ -1,6 +1,29 @@
 #ifndef __UTILS_H
 #define __UTILS_H
 
+#include <stdbool.h>
 
+// Print usage text.
+void print_usage_text();
+
+// Set CLI argument.
+// Parameters:
+//  - key       - argument key (without leading dash)
+//  - value     - argument value as string
+// Returns:
+//  - true on success
+//  - false on failure
+// Remarks:
+//  - neither key nor value are copied, they are saved as pointers
+//  - use this function only with data from argv
+bool cli_arg_set(const char *key, char *value);
+
+// Get CLI argument.
+// Parameters:
+//  - key       - argument key (without leading dash)
+// Returns:
+//  - pointer to the value (not owned by you)
+//  - NULL on failure
+const char *cli_arg_get(const char *key);
 
 #endif