Add validators for built-in formats

[jacksmith15]

JSONSchema specifies several preset values for the "format" keyword for validating strings, along with the validation logic they should perform. "uuid" and "date-time" are already implemented, the following are not:

• "time"
• "date"
• "email"
• "idn-email"
• "hostname"
• "idn-hostname"
• "ipv4"
• "ipv6"
• "uri"
• "uri-reference"
• "iri"
• "iri-reference"
• "uri-template"
• "json-pointer"
• "relative-json-pointer"
• "regex"

The correct validation logic for each is specified here.

Currently only validation for "date-time" and "uuid" is enabled (see here).

The remaining format validators should be implemented here.

An example test for "uuid" can be found here.