quadratic_probe_fn Interface

# `quadratic_probe_fn` Interface

A probe sequence policy using square increments.

1. `hash_policy.hpp`
2. Template parameters.
3. Public Types and Constants:
   1. General definitions.
4. Public Methods:
   1. Constructors, destructor, and related.
5. Protected Methods:
   1. Offset methods.

## Template parameters.

Parameter | Description | Default Value
    Const_Key_Ref
| Const key reference type. | -
    Size_Type
| Size type. | size_t

## General definitions.

Type | Definition | Description
    size_type
    Size_Type
| Size type.

## Constructors, destructor, and related.

Method | Description
    void
      swap
      (quadratic_probe_fn &r_other)
| Swaps content.

## Offset methods.

Method | Description
    inline size_type
      operator()
      (Const_Key_Ref r_key,
        size_type i) const
| Returns the `i`-th offset from the hash value.