Assignment by [-,+,*,/,**], power-op is completed.

Assignment by:
> `a += 5;`  |  `a /= 5;`  |  `a *= 5;`  |  `a **= 5`   |   `a -= 5`

Supports numeric types.
PS: `+=` supports increasing pointers, and can be used for string concentration.
PS: `-=` supports decreasing pointers.

The power operator was incomplete, no evaulation was made for them, only
the parsing/tokenizer was finished.