Restructure config module for easier addition of items

components/config/config.h

@@ -8,12 +8,12 @@
 
 #include <stddef.h>
 
-#define MAX_HOSTNAME_SIZE 32
+#define CONFIG_MAX_VALUE_SIZE 32U
 
 /**
- * Callback type for consumers of string settings.
+ * Callback type for config updates
  */
-typedef void (*ConfigStringCallback)(const char *value);
+typedef void (*ConfigCallback)(const char *value);
 
 /**
  * Initialize the configuration module.
@@ -21,7 +21,7 @@ typedef void (*ConfigStringCallback)(const char *value);
  * If there is a saved configuration, it will be loaded. Otherwise,
  * the default configuration will be loaded and saved.
  */
-void config_init();
+void config_init(void);
 
 /**
  * Set the device's hostname.
@@ -49,6 +49,6 @@ size_t config_get_hostname(char *buffer, size_t buffer_size);
  * lifetime of the passed argument will be static, but the value may
  * be modified once the callback returns.
  */
-void config_add_hostname_callback(ConfigStringCallback callback);
+void config_add_hostname_callback(ConfigCallback callback);
 
 #endif