feat: support const and examples

[csimi]

const was added in JSON schema draft 6: https://json-schema.org/understanding-json-schema/reference/generic.html#constant-values
I see that "example" is supported on the OpenAPI level but it should also be supported in the JSON schema: https://json-schema.org/understanding-json-schema/reference/generic.html#annotations

[XVincentX]

@RomanHotsiy Any chance to get this merged?

[RomanHotsiy]

Sorry, super busy. I will check this on weekends

[XVincentX]

Fantastic — this would really help us!

[XVincentX]

@RomanHotsiy Have you been able to check this out?

[RomanHotsiy]

LGTM 👍 Thanks.
Will release a new version on weekends.

[RomanHotsiy]

fyi: already released 1.0.0-beta.15

[XVincentX]

Oh fantastic, I'll try this out!

[XVincentX]

@RomanHotsiy I can't find it on npm 🤔

[RomanHotsiy]

Whoops, looks like I have to update npm key on Travis. Deployed manually. Should be on npm already!