Flex Validator: Validate request values based on extensible rules

This package can validate request values based on extensible rules.

It provides a class that can validate request values given the array of the request parameters to be checked and a list of rules that should be evaluated to perform validation.

Currently it implements built-in rules like:

- Required non-empty value
- Value is the same as another given field
- Value is between a range
- Value is not less than a minimum
- Value is not more than a maximum
- Numeric value between a range
- The value is confirmed or accepted
- A valid domain
- A time before or after a value
- Made of letter, or digits, or letters and digits including dashes
- Valid date in a given format
- Valid email address
- Valid IP address
- Valid URL
- Is an integer
- Matches a regular expression
- The value is one of a given list
- The value is not one of a given list
- A file with a size smaller or larger than a limit
- A file with one of a list of allowed MIME types

The validation rules may be extended with custom rules defined by callback functions that check the values.