[Revamp] Add arithmetic expressions

[kishtarn555]

Add sum, subtraction, multiplication, integer division, modulo and parenthesis

void mult(x,y) {
  iterate(x*(y+1)) {
    putbeeper();
  }
}

[ccepeda]

As with other changes this would quickly turn Karel tasks into C++ easy tasks and in such case there is little point in learning Karel.

Lets leave this in standby

[kishtarn555]

As an alternative that just came to mind, that I'll leave here for future reference. We could add a built in method mult(n) that multiplies n by the floor value and leaves it in the ground.

Same with division

Though I agree having to code your own division/multiplication has a Karel-charm to it