fix: use empty cancellation reason as default

[dankeboy36]

Let clients conveniently cancel the token without any reason.

---

The cancellation works very nicely. Thanks for the great work, Dennis!

This PR proposes an API change to let clients cancel the token without a reason.

Before:

useEffect(() => {
    const token = new CancellationTokenImpl();
    search(query, filter, token);
    return function () {
        token.cancel('');
    };
}, [search, filter, query]);

After:

useEffect(() => {
    const token = new CancellationTokenImpl();
    search(query, filter, token);
    return function () {
        token.cancel();
    };
}, [search, filter, query]);

[dhuebner]

@dankeboy36
Thank you for this contribution!
I wonder if we should also make the listeners parameter optional.

Instead of defaulting the reason to an empty string like you proposed public cancel(reason = ''): void make the parameter optional public cancel(reason?: string): void and adjust the callback signature to be callback: (reason?: string) => void . In other words make it more explicit to the listener implementors that the reason might not be provided.

[dankeboy36]

I was about to make the requested changes when I saw 6e2df6f. Sorry for the delay, and thanks!

[dhuebner]

@dankeboy36
A new v0.5.1 version with optional reason parameter was published.