Deprecate support for configuring validation options

[seanpdoyle]

In preparation for #31, this commit deprecates support for global
and matcher-specific options, like strict: true.

The json_schema gem does not accept similar configuration
options, so in the future we'll need to remove support entirely.

[houndci-bot]

Style/MutableConstant: Freeze mutable objects assigned to constants.

[mike-burns]

I don't know what it means for me to ask this: do we want to use ActiveSupport::Deprecation?

[seanpdoyle]

@mike-burns in order to use ActiveSupport::Deprecation, we'd have to add a dependency on activesupport.

Right now, activesupport is only a development dependency.

What does ActiveSupport::Deprecation provide that is an improvement on warn?

[mike-burns]

AS::Deprecation warnings can be silenced the same way any other Rails deprecation notice can, whereas warn requires -W0 to silence it.

If we don't depend on AS, then let's not add it just for this.

[seanpdoyle]

Merged in f840139.