allow line break at operators

[Yingjie Lan]

:And if we require {} then truly free indentation should be OK too! But

:it wouldn't be Python any more.

Of course, but not the case with ';'. Currently ';' is optional in Python,
But '{' is used for dicts. Clearly, ';' and '{' are different in magnitude.

So the decision is: shall we change ';' from optional to mandatory
to allow free line splitting?

Yingjie