Implicit type conversion

Since version 3.00, all the number types (int, rat, float and complex) are unified in the Number class and all the needed conversions are done implicitly. Methods from other classes also make implicit conversions where possible.

> 1+"2"            #=> 3
> "1"+2            #=> 12
> sqrt(-4)         #=> 2i
> ("a" + [1,2])    #=> a[1,2]
> ('ha' * '3')     #=> hahaha
> ('ha' * true)    #=> ha