Add baked in validators for containsfield and excludesfield

[fharding1]

• Tests exist or have been written that cover this particular change.

Change Details:

• Adds containsfield baked in validator, as well as tests and documentation for containsfield.
• Adds excludesfield baked in validator, as well as tests and documentation for excludesfield.

@go-playground/admins

[coveralls]

Coverage remained the same at 100.0% when pulling 80d96ab on fharding1:baked-in-contains-excludes-field into 6079fcc on go-playground:v9.

[fharding1]

I considered making these validators panic on non-string types but it looks like that isn't the behavior of other validators so I decided against it. I also considered adding support for fmt.Stringer but did not for the same reason.

[deankarn]

Hey @fharding1 thanks for the PR!

I just have one request, can it be renamed to fieldcontains and fieldexcludes?
I was confused by the naming, I was reading it as if it was checking that the actual field was contained in the struct rather than containing the value.

[fharding1]

@joeybloggs thanks for the feedback, done.

[fharding1]

bump @joeybloggs

[deankarn]

sorry @fharding1 got sick after the holidays and now the family is sick, trying to catch up on all this, sorry for the delay

[fharding1]

No worries, I don't mean to be a bother, I just figured after a month you might have forgotten about it. Hope you and your family feels better soon!

[deankarn]

@fharding1 no worries, I do forget sometimes too ;)

[axiaoxin]

excludesfield is still on godoc https://godoc.org/github.com/go-playground/validator#hdr-Field_Excludes_Another_Field

[jtyoui]

😔 excludesfield and containsfield is still on godoc, this keeps reporting errors.
https://godoc.org/github.com/go-playground/validator#hdr-Field_Excludes_Another_Field