Laconia#48 - Ignore if callback is falsy

[hugosenari]

Partially solves #48
Changes:

1. Use return when callback is falsy;
2. Introduce a configuration that we eventually deprecate i.e. LACONIA_NO_CALLBACK = true;

Things to do after that (for other PRs):

1. Update documentation with LACONIA_NO_CALLBACK;
2. Add warning for deprecations of callback usage;
3. Rewrite batch to work without callback;
4. Remove anything (configs, warning and callback).

[ceilfors]

Hey @hugosenari. Thanks for this PR. I personally feel that it's quite difficult to ask our users to add more boilerplate code to get rid of the warnings.

The solution from @geoffdutton might work more seamlessly for our users if you want to fix this issue. Although bear in mind that it triggered test failures (I can't remember in detail now), which I have documented here. I suspect that it might just test configuration issue.

[hugosenari]

I know, I have another branch for @geoffdutton solution and found where is the fail point, but it breaks API.

Options:

1. Update major version (accept the breaking changes);
   • We need rewrite laconia/batch to use Async/Iterator;
2. Create another entrypoint (ie: @laconia/core/async);
   • Leaves laconia/batch using legancy api.

And is not just warnings, annoys me that I need set context.callbackWaitsForEmptyEventLoop to false because we are using callbacks, thats why I suggest that if we don't have callback, we don't use it. And since it will be a common pattern (unless we break api) create built-in boilerplate to do that. 😄

[hugosenari]

Updates:

• Removed: async wrapper
• Introduce a configuration that we eventually deprecate i.e. LACONIA_NO_CALLBACK = true, as @ceilfors suggested.

[FrancoMeriles]

This will come out in the next release ?

[hugosenari]

closing this in favor of: #511