Document new Validation API options?

[weaverryan]

Hi guys!

Related to https://github.com/symfony/symfony/blob/master/UPGRADE-2.5.md#validator and https://github.com/symfony/symfony/blob/master/UPGRADE-3.0.md#validator - specifically, I'm talking about the new Validator API and options.

Needed changes:

• A) Update the ExecutionContextInterface namespaces (see Update Callback.rst #4161 and 2.5 Validation API changes #4233)
• B) Update the addViolationAt to buildViolation
• C) Add a cookbook entry to explain all of this stuff, and show how a bundle can support both versions
• D) Update the framework reference section with the framework.validation.api option.
• E) Replace usages of deprecated method validateValue() where needed.
• F) Change signature of using ->validate with a group argument:

[weaverryan]

Related:

• Replace addViolationAt (deprecated) by buildViolation #4056
• Don't use deprecated functions in Callback.rst #4105
• Update Callback.rst #4161

[xabbuh]

#4242 is also related.

[mvar]

+1

[wouterj]

1 fixed, 5 to do :)

[xabbuh]

"A" is already fixed (see #4161 and #4233).

[xabbuh]

"E" is no issue at all (we don't use validateValue() anywhere).