Auto-multiplication support to Mate(arithmetic expression parser)

By PR [#19](https://github.com/theiskaa/mate/pull/19). Mate, now, can automatically understand and parse auto-multiplication needed cases.

For example: 5(5 / 2) is same as 5 * (5 / 2), In this case, to make calculator understood this expression, we have to add a PRODUCT(multiplication) token manually between two token numbers. (in this case between 5 and (5 / 2)).