Incompatible with previous (pre-release)

Changes:

• Specs class renamed to SpecCollection.
• Exceptions split out into their own files and renamed:
  • Validate\ValidationException => Validate\Exception\ValidationException
  • Validate\ValidationNamedCheckException => Validate\Exception\NamedValueException
• Improve bad input checks in Validate.
• Validator option empty_null renamed to the more descriptive null_empty_strings. Using the old name will still work but will trigger a deprecation warning.
• Validator option empty_delete (was default true) renamed to the more descriptive delete_null (now default false). Using the old name will still work but will trigger a deprecation warning.
• Validate option nocase renamed to the more descriptive allowed_values_nc. Using the old name will still work but will trigger a deprecation warning.