Add enforce.arrayOf() rule

[ealush]

This rule can be quite useful when a future schema validation rule will be added to enforce.

The general idea is quite similar to the enforce.any rule:

enforce(value).isArrayOf(
  enforce.isString(),
  enforce.isNumber(),
 enforce.isArrayOf(...) // Yeah, why not? A recursive call should be pretty simple here
)

The idea is that at least one needs to be truthy in order for the condition to be met - alternatively, an empty array should probably be valid as well unless explicitly mentioned:

enforce(value).isArrayOf(
  enforce.isString()
).isNotEmpty()

See Shape for reference.

[Moses3301]

#499 implement isArrayOf rule

[ealush]

Closed by #499