small fixes for command name loading

new readme with ref to github wiki
improve performance of command lookup.
Fix cmd type and object type in cached queries.
Support for MySQL 5.5.21 offsets

src/MySQLPlugin.map

@@ -0,0 +1,10 @@
+{
+	global:
+		_mysql_plugin_declarations_;
+		_mysql_plugin_interface_version_;
+		_mysql_sizeof_struct_st_plugin_;
+		audit_plugin_so_init;
+		thd_alloc_service;
+
+	local: *;
+};