Move almost all filter command code to cmd_* subroutines

Move almost all filter command code to cmd_* subroutines

For example '/FILTER VERSION' (sub)command is now dispatched from
filter_command_handler to cmd_version() subroutine.  The exceptions
are ON. OFF, ALLOW and HELP subcommands (with to short code to bother
separating into subroutine); and SERVERON and ALL which reuse
cmd_server_limit() subroutine; and SAVE and LOAD commands which use
save_filter() and load_filter() subroutines, respectively.

While at it correct output about finishing loading script, and bump
version to 2.0.4

Signed-off-by: Jakub Narebski <jnareb@gmail.com>