Add new features to logger plugin (command /logger, log level, level by buffer, mask by buffer, ..), fix some bugs

New features:
- new command /logger
- log level, to log only some messages, according to importance (task #8592)
- level by buffer: custom level for some buffers (or group of buffers)
- log filename mask by buffer (or group of buffers)
- marker line is added after display of backlog
- add "delete" callback for config file sections
- add "mkdir_parents" function to plugin API
- remove old log options in IRC plugin

Bug fix:
- marker line is set only when user switches buffer (not when a plugin force
  switch, like IRC plugin does when opening server or channel buffer)
- backlog fixed (sometimes lines were not properly displayed)

src/plugins/scripts/script-api.h

@@ -51,7 +51,12 @@ extern struct t_config_section *script_api_config_new_section (struct t_weechat_
                                                                                              struct t_config_section *section,
                                                                                              const char *option_name,
                                                                                              const char *value),
-                                                               const char *function_create_option);
+                                                               const char *function_create_option,
+                                                               int (*callback_delete_option)(void *data,
+                                                                                             struct t_config_file *config_file,
+                                                                                             struct t_config_section *section,
+                                                                                             struct t_config_option *option),
+                                                               const char *function_delete_option);
 extern struct t_config_option *script_api_config_new_option (struct t_weechat_plugin *weechat_plugin,
                                                              struct t_plugin_script *script,
                                                              struct t_config_file *config_file,
@@ -136,7 +141,7 @@ extern struct t_hook *script_api_hook_print (struct t_weechat_plugin *weechat_pl
                                                              struct t_gui_buffer *buffer,
                                                              time_t date,
                                                              int tags_count,
-                                                             char **tags,
+                                                             const char **tags,
                                                              const char *prefix,
                                                              const char *message),
                                              const char *function);