Add IO_NUMBER to Tokenizer

Signed-off-by: Oleg Bulatov <oleg@bulatov.me>
Handle IO_NUMBER

Signed-off-by: Oleg Bulatov <oleg@bulatov.me>
Rename Command into SimpleCommand

Signed-off-by: Oleg Bulatov <oleg@bulatov.me>
Add CompoundCommand

Signed-off-by: Oleg Bulatov <oleg@bulatov.me>