Add custom json formatter for format: date

[kMutagene]

See #240.

@sergey-tihon @Thorium I gave this a shot by adding a custom attribute if the format of a string in the schema is date.

I could not get the test projects to work locally, but i would guess i could add a controller to the swashbuckle webapi?

E.g. a UpdateDateOnlyController here https://github.com/fsprojects/SwaggerProvider/blob/master/tests/Swashbuckle.WebApi.Server/Controllers/UpdateControllers.fs

If you could give me guidance on where and how to add relevant tests that would be great.

[sergey-tihon]

Thank you for this PR @kMutagene.

but i would guess i could add a controller to the swashbuckle webapi?

yes, we need to find out how to create a controller that emits schema with such a date-time format.

E.g. a UpdateDateOnlyController here

Yes, you can create a new one for date-time special cases or use SpecialCasesControllers.fs

If you could give me guidance on where and how to add relevant tests that would be great.

The simplest option is to extend SpecialCasesControllers.fs, and then add new test to Swashbuckle.SpecialCasesControllers.Tests.fs