feature: support form errors (see issue #15)

[bkinsey808]

What are you adding/fixing?

I love the syntax of ngxErrors so much, that I wanted to use it not just for form control errors, but for form errors itself. See issue #15

Have you added tests for your changes?

I'm sorry, I did not. But the existing tests still passed.

Will this need documentation changes?

Yes, I imagine this feature is something ppl would want to know about.

Does this introduce a breaking change?

I don't think so. As far as I can tell, all existing functionality still remains.

Other information
This code is a bit ugly, not super DRY. I sort of intended it as a proof of concept. It could be cleaned up and refactored, maybe we need a concept of a single object that can be either a form control or a form group. I'm especially displeased with having to call detectChanges() but I haven't found a way around it for OnPush change detection strategy. If anybody knows how to avoid it, pls let me know, I want to learn.

Thanks @toddmotto for a great project!

[listepo]

@toddmotto can you check this PR?

[toddmotto]

We'll get this baked into a future addition of ngxErrors - planning to enhance some of the internals and there's a few things in here which work but what I'd like to do is introduce this feature once we've re-shapen the internals. This will make things a little smoother as there's a few hacks in here to get things to work - we'll add :)

[listepo]

@toddmotto thanks

[DmitryEfimenko]

Also looking forward to this feature.

[picosam]

Hello @toddmotto would love to know if you've got a timeline for this?

[listepo-alterpost]

@toddmotto any news?

[JustinElst]

this looks interesting!