support num command

[akiradeveloper]

In vi, user is able to repeat a command multiple times by num followed by the command (e.g. 4x to remove the character 4 times).

Currently, recognizing the num part is only to JUMP node on FSM. To make it possible for num part to cooperate with other commands, we may need to move the num part to INIT node, or add new edge from JUMP node (should be renamed to NUM btw).

Anyway, the change should be undoable atomically and the concept of change log set is implemented in prior.