Channel resumed parameter now has to be non-null

[ikurek]

This is supposed to fix bug #297, the original fix was issued on #270 but I don't think the approach there was correct, so I changed a few things.

The issue was caused by this definition of Obj-C macro:

#define WRITE_VALUE(DICTIONARY, JSON_KEY, VALUE) { 
    if (VALUE) {
        [DICTIONARY setObject:VALUE forKey:JSON_KEY];
    } 
}

which is supposed to write JSON key only if VALUE parameter is not nil. By accident, if the parameter is not nil, but it happens to be 0 or any other falsey value, the key also isn't written 😆 I've updated the base method to only check for nil and also write false values.

The other error was with tenary operators and booleans. The expression:

[stateChange resumed]?@([stateChange resumed]):nil

evaluates to nil if resumed is nil or false, therefore false values were never written 😄