Forbid whitespace in operator names

[masak]

This will make 007 conform a bit better with Perl 6. And it'll be less confusing. ("Visual pill" and all that.)

We'll have to change the not in operator in examples/in.007. I suggest renaming it !in. In the fullness of time, that might be supplied via an infix-prefix negating metaoperator.

Note that Python has not in (and is not). I consider it one of Python's very few weird eccentricities. Guess Python's grammar is so neat and orderly everywhere else that they get away with a little bohemian craziness here.

Note also that this doesn't affect is parsed operators such as ?? !!. Except that the name of the operator cannot now be infix:<?? !!> with a space in it. Unless we make an exception for is parsed operators...?