Filtering by sql_command for audit plugin

Description
===========

  - add option `audit_log_include_command' to specify commands to log.
  - add option `audit_log_exclude_command' to specify commands to
    exclude from logging.

  Example:

  ,----
  | SET GLOBAL audit_log_include_commands= 'set_option,create_db';
  | SET GLOBAL audit_log_exclude_commands= 'set_option,create_db';
  `----

  List of commands:

  ,----
  | mysql> select name from setup_instruments where name like "statement/sql/%" order by name;
  | +------------------------------------------+
  | | name |
  | +------------------------------------------+
  | | statement/sql/alter_db |
  | | statement/sql/alter_db_upgrade |
  | | statement/sql/alter_event |
  | | statement/sql/alter_function |
  | | statement/sql/alter_procedure |
  | | statement/sql/alter_server |
  | | statement/sql/alter_table |
  | | statement/sql/alter_tablespace |
  | | statement/sql/alter_user |
  | | statement/sql/analyze |
  | | statement/sql/assign_to_keycache |
  |
  | ...
  `----

  *NOTE*

  Invocation of stored procedure has `sql_command' field
  "call_procedure". All statemets within the procedure have
  `sql_command' "call_procedure" as well.