the time is now: fix class static variables

[gewang]

class Foo
{
    5 => static int x;
    static SinOsc y;
    new SndBuf @=> SndBuf @ z;
}

possible semantics and process:

1. identify lines with static variables
2. disallow both static and non-static variables in the same line
3. disallow time-advance (could be a compiler error or a runtime exception for immediate mode violation) (e.g., 1::second => static dur a => now;)
4. run the static lines a) at compile-time if public class OR b) at run-time if non-public class

int x;

fun int bar()
{
    return x+5;
}

class Foo
{
    bar() => static int z;
}