Go library for struct and field validation

 The validator package implements value validations for structs and
 individual fields based on tags.
 .
 It has the following unique features:
  - Cross Field and Cross Struct validation by using validation tags
    or custom validators.
  - Slice, Array and Map diving, which allows any or all levels of a
    multidimensional field to be validated.
  - Ability to dive into both map keys and values for validation.
  - Handles type interface by determining its underlying type prior
    to validation.
  - Handles custom field types such as the SQL driver's Valuer.
  - Alias validation tags, which allows for mapping of several
    validations to a single tag for easier definition of validations
    on structs.
  - Extraction of custom defined Field Name, allowing to specify
    extracting the JSON name while validating and making it available
    in the resulting FieldError.
  - Customizable i18n-aware error messages.