[FEATURE] Simplify early returns

[michaelboyles]

It might be desirable to return early within a reducer, for example

interface State {
    str: string;
}

const val = 3;
const reducer = redcr((state: State) => {
    if (val == 3) {
        state.str = 'abc';
        return;
    }
    state.str = 'def';
});

As redcr()'s signature accepts a void-returning function, it might be expected that this will work. However, the output is

const reducer = (state) => {
    if (val == 3) {
        state = { ...state, str: 'abc' };
        return; // <<< should be   return state;
    }
    state = { ...state, str: 'def' };
    return state;
};

The first branch will end up returning undefined. A workaround exists: the author can specify return state; rather than return; but maybe that's unintuitive since the function is supposed to be void-returning.

Somewhat related to #14